Cast Iron VS Malleable Iron: What's the Difference?

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Malleable Fitting

Malleable iron, just like cast iron is produced by a casting method but they are actually quite different from each other. Although, Malleable iron fittings start out as a cast iron fittings, they are then transformed into a much more durable malleable iron through a heating process.

Although they both contain iron, there is a major difference between malleable iron and cast iron. The main difference being that malleable iron is, well, malleable and cast iron is not. But there are other differences as well. We&#;ll need to talk about what exactly these metals are and how they are made.

In this post, we will clear up any confusion between malleable iron and cast iron and go through the different materials that fall under the cast iron umbrella. We will explain what sets malleable iron apart and what applications best suit each material. Let's take a look.

What is Cast Iron?

Cast iron is the result of smelting ore in a furnace, creating pig iron that has a high carbon content. Alloys are then added to the iron which is poured into molds and allowed to cool.

Cast Iron

Due to their extreme brittleness, cast iron fittings should never be used in plumbing applications. Understanding the difference is key to ensure you are selecting the correct material fitting for your application. Below, we have four materials that fall under cast iron, grey, white, malleable and ductile.

Grey Cast Iron

Grey cast iron is not the material used to make cast iron or malleable fittings. Grey cast iron gets it's name from the grey appearance that the fractures of the material give off. Grey cast iron is the most commonly used cast iron and is the most widely used cast material due to the weight. Grey cast iron's strength is comparable to low or medium carbon steel, but it has less tensile strength and shock resistance compared to steel. Common items made from grey cast iron are well caps and well seals.

White Cast Iron

White cast iron was used in both cast iron and malleable iron fittings. White cast iron has a presence of cement that gives off a white surface, hence the name. White cast iron is too brittle for many structural applications but with it's good hardness and abrasion resistance, it can be used in many applications including teeth of a backhoe's digging bucket and lifter bars in ball mills. This material is also relatively low cost.

Malleable Cast Iron

Malleable iron starts out as white iron casting but is then treated at a heat of roughly 1,650°F, 900°C. Malleable iron contains more blunt boundaries opposed to flakes, which eliminates the stress concentration problems that grey cast iron can cause. Malleable iron has properties that are very similar to mild steel.

Ductile Cast Iron

Ductile cast iron is a more recent development. Small amounts of magnesium is added. Ductile iron is very similar to malleable iron, but parts can be cast larger compared to malleable iron where there is a limit of how large the part sections can be cast. Blue, electrostatic epoxy paint is added to items like pitless spools, well seals and well caps for corrosion resistance.

What is Malleable Iron?

Round Flange with 4 Bolt Holes

Malleable iron starts out as cast iron, but an annealing heat treatment is applied to the cast iron to make it more workable and increase ductility. Consequently, malleable iron has a much lower carbon content than cast iron. There are three different types of malleable iron:

&#; Blackheart

&#; Whiteheart

&#; Pearlitic

Production

To make malleable iron, foundry workers add hematite ore during the annealing process. Depending on the need for ductility, they may also add sodium, cerium, or magnesium.

Cast iron is typically smelted in a bloomery. Usually, the furnace becomes too hot for other types of iron making and this is when the iron absorbs the most carbon. It is then poured into molds for cooling.

Properties

Malleable iron is easier to work with to make more intricate designs, such as Malleable Iron Pipe Fittings. On the other hand, cast iron is better known for its castability, meaning it is easily poured into molds without premature cooling because of its low melting point.

Composition

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The annealing process of malleable iron causes it to form small particles of carbon that are shaped irregularly. This gives the iron more strength while allowing it to keep ductility. Malleable iron is relatively easy to machine, and it is shock resistant.

Cast iron contains about two percent carbon, which makes it stronger and more resistant to rusting. But this also makes it more difficult to machine because it is difficult to get a smooth surface with the material. This can also make cast iron more costly to work with as it reduces tool life.

Cost

Both cast iron and malleable iron are similarly priced. However, cast iron tends to be cheaper because it has a low melting point requiring less energy to heat it.

Function

Cast iron is used to make castings such as barbell weights in a gym or engine blocks.

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The cast iron vs malleable iron will be discussed in this article. When selecting the proper material for a given task, it is vital to comprehend the difference between various types of metals. Cast iron and malleable iron are two used materials. With knowledge of their respective properties and functions, you will be able to make an informed choice of which one to use. This will help you determine which metal is ideal for your project.

What Is Cast Iron?

A category of iron alloys known as &#;cast iron&#; generally comprises 2% to 4% carbon. It may even reach 5%, depending on the specific variety of cast iron. Various waste metals and alloys are combined with smelted iron ore or pig iron to produce them. Cast or pour the molten substance afterward. It retains its strength while solidifying into the shape of the mold. Due to its high carbon ratio, unique erosion resistance, and strength are characteristics of cast iron.

Types Of Cast Iron 

The following four materials are classified as cast iron: grey, white, malleable, and ductile.

1. Grey Cast Iron

Composition:

• 1-3% silicon, rest iron
• 5-4% carbon

Grey cast iron is not used to produce malleable fittings or cast iron. The gray shade emitted by the fractures of grey cast iron is the source of its WS40 (top)-1 designation. Due to its weight, grey cast iron is the most utilized, and the most used released WTCC-6-CI material.

Grey cast iron possesses strength like that of low or medium-carbon steel. Moreover, it is weaker tensile strength and impact resistance. Seals and well caps are ordinary objects fabricated from grey cast iron.

2. White Cast Iron

Composition:

• 3%-L8 silicon, rest iron
• 8-3.2% carbon

Both cast iron and malleable iron fixtures were fabricated from white cast iron. The uniform white surface of white cast iron is due to the cementous substance present in it. For many structural applications, white cast iron is excessively brittle.

Still, its good hardness and abrasion resistance can be used in many applications. These include the backhoe&#;s digging bucket and lifter bars in ball mills. This material is also relatively low-cost.

3. Malleable Cast Iron

Composition:

• 3%-1.8 silicon, rest iron
• 8 -3.2% carbon

2-BLB-Malleable iron starts as white iron casting. However, it was treated at a temperature of roughly 1,650°F, 900°C. Malleable iron contains blunter boundaries than flakes. Grey cast iron can cause problems with stress concentration, but this iron doesn&#;t. Comparable properties can be found in malleable iron and mild steel.

2-BLB- After heating to about 1,650°F (900°C), malleable iron transforms from its original state into white iron casting. The lack of flakes in malleable iron prevents stress concentration issues that might arise from grey cast iron. A lot of the characteristics of mild steel are shared by malleable iron.

4. Ductile Cast Iron

Composition:

• 6% to 2.8% silicon, 3% to 4% Carbon, and the rest iron
• A meager amount of sulfur and phosphorus

The development of ductile cast iron occurred very recently. A tiny quantity of magnesium is included. While both ductile iron and malleable iron have comparable properties, they allow for the casting of bigger components, while the latter has the most allowed sectional size. Pitless spools, well seals, and well caps are coated with blue electrostatic epoxy paint. It helps to make them corrosion-resistant.

What Is Malleable Iron?

Annealing is the thermal process by which malleable iron is produced. Workability and flexibility are both enhanced, while carbon content is decreased using this technique. Various cast irons, including white cast iron with a high carbon content, are first cast. The transformation of carbon into graphite occurs when it is heated for a long time to a temperature below its melting point.

Nodules or spheres, the end product of this process, make cast iron so pliable. When metal is annealed, its brittleness decreases, making it more resistant to cracks. It allows for shaping and bending without fracturing.

Types Of Malleable Iron:

• Pearlitic
• Blackheart
• Whiteheart

Cast Iron Vs. Malleable Iron

&#; Differences in Formation

The initial step in producing malleable iron is the rapid cooling of cast iron to produce white cast iron, thereby inhibiting the deposition of graphite particles. Using particular substances, the white cast iron is heated for extended periods. Throughout these intervals, a portion of the carbon present in the iron undergoes decomposition and starts to separate from the metal, transforming into graphite particles. Further addition of liquid metal is required to prevent fractures caused by volume loss. This process yields malleable iron.

Utilizing a bloomery furnace, one can produce cast iron. The metal is never transformed into a liquid state by melting iron in a bloomery furnace via direct reduction. Gray cast iron is created when the iron incorporates an adequate amount of carbon when the furnace temperature exceeds the limit set for other varieties of iron casting. As it cools, graphite particles are produced.

&#; Carbon Ratio

Malleable iron comprises carbon ranging from 0.08% to 0.20% by weight. In contrast, cast iron has a higher carbon content than malleable iron. The carbon content of the substance varies between 2 and 4.5 percent.

&#; Properties

For intricate designs, such as malleable iron pipe fittings, malleable iron is easier to manipulate. Cast iron is more recognized for its castability, which refers to its capacity to be easily poured into molds. It does not require cooling due to its low melting point.

Cast Iron Advantages

The pros of cast iron are as follows.

• Materials composed of cast iron (Grey Cast Iron) are machinable.
• It possesses excellent casting properties.
• Cast iron possesses a compressive strength that is three to five times greater than that of steel.
• Cast iron possesses exceptional corrosion resistance.
• It possesses low-pressure concentration and resistance to deformation.

Cast Iron Disadvantages 

The following disadvantages pertain to cast iron.

• Cast iron is exceptionally brittle.
• Machining is not possible with white cast iron.
• Its resistance to impact is inadequate, and its weight-to-strength ratio is high.
• Machinability is weak.

Advantages of Malleable Cast Iron

When is malleable cast iron appropriate for a given application? When these benefits are required:

• A ductile material is well-suited for applications requiring substantial machining during refining. Its tensile strength, elasticity, and impact resistance are lower than ductile iron&#;s. However, it can still be machined without fracturing.
• It can be hammered and flattened, in contrast to certain cast irons, which would fracture or shatter.
• Robust as gray cast iron.
• Excellent resistance to impacts at low temperatures.

Disadvantages of Malleable Cast Iron 

There are disadvantages to the physical properties of malleable cast iron. Always be aware of a material&#;s drawbacks:

• Shrinks due to volume loss when cooled. This occurs to some degree with all cast irons and all materials, but it is especially evident with malleable cast iron.
• Corrosion resistance is low.
• It is less durable than steel or ductile cast iron.
• It can become brittle at high temperatures, rendering it susceptible to splitting. Thus, it should not be used for high tensile or compressive strength applications.

Summary

Knowing each element of facts ensures that the proper material is utilized. However, each material has specific applications in which it functions effectively. Malleable iron is used in the plumbing industry, where it has gained considerable popularity.