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What Is Ductile Iron?

Nov. 21, 2020
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Ductile Iron is a kind of cast iron, which has the characteristics of impact resistance, fatigue resistance, elongation and wear resistance due to the spherical (round) graphite structure in the metal. Ductile cast iron is also called ductile cast iron, spheroidal graphite cast iron, or nodular cast iron.

What makes ductile iron "spheroidal graphite cast iron"?

Both ductile iron and cast iron contain graphite. If you look closely (using a high-power microscope with a magnification of 100x or higher) on ordinary cast iron (gray iron), you will find that graphite drill bits look like curved lines, called "flakes". However, when you look at the graphite in ductile iron, they look like small spheres or nodules (hence the names of spherical graphite iron and ductile iron).

We attribute the achievements of Keith Millis to the manufacture of ductile iron in 1943. He and his partners Albert Gagnebin and Norman Pilling were awarded US patents 2,485,760 and 2,485,761 for using magnesium (Mg) in metallurgy to make ductile iron. In the secret recipe) arrange the graphite into a spherical shape.

However, ductile iron has become one of the most popular types of cast iron. The development of nodular cast iron continued until the 1950s, making the casting process of nodular cast iron better developed, leading to the acceptance of nodular cast iron. In the 1960s, as an engineering material for engineering applications, its usage increased by 9 times, proving the acceptance of ductile iron.

How is nodular iron made?

Most of the magic of making ductile iron takes place in iron melting and furnaces. You start with iron (of course), and then add more carbon than iron normally absorbs into the structure. Explaining the iron-carbon relationship in another way is like adding too much salt to the water so that no more salt will dissolve. By the way, this is what makes ductile iron different from steel. Steel only absorbs the carbon that iron can absorb.

Silicon, sulfur, manganese, and oxygen all play a role in the mixture to help the carbon form a spherical graphite structure as the iron cools.

What is in ductile iron? (Composition)

If you want to chemically analyze ductile iron, you will usually find the following:

  • Iron ~94%

  • Carbon 3.2 – 3.60%

  • Silicon 2.2 – 2.8%

  • Manganese 0.1 – 0.2%

  • Magnesium 0.03 – 0.04%

  • Phosphorus 0.005 – 0.04%

  • Sulfur 0.005 – 0.02%

  • Copper <= 0.40%

In order to increase the strength of ductile iron, additional tin or copper can be added. In order to improve corrosion resistance, copper, nickel or chromium can replace 15% to 30% of iron.

 

What are the benefits of ductile iron?

Compared with ordinary cast iron (gray cast iron), ductile cast iron is very strong. The tensile strength of cast iron is 20,000-60,000 pounds, while ductile iron starts at 60,000 pounds and can go to 120,000 pounds. The yield strength of ductile iron is usually 40,000-90,000 psi, but the yield strength of cast iron is so low that it cannot be measured.

Let us use our strength in different ways. We have already seen that gray iron parts will break after falling ten feet and hitting the ground. Using ductile iron castings, you can hit the parts with an eight-pound octagonal hammer all day without cracking.

The cause of the gray iron problem is that the graphite flakes promote the fracture of the graphite flakes, and the nodules in the ductile iron keep the iron together. Given the identical situation of the same part made of two different metals, brittle gray cast iron wants to crack, while ductile iron wants to bend.

Due to the graphite in ductile iron, ductile iron also has excellent wear resistance. When you rub on ductile iron, ductile iron wears much slower than many other metals. The wear resistance partly comes from the graphite structure, which can act on iron like a dry lubricant.

Nodular cast iron can also dissipate heat well (eliminate heat) and can be easily machined, although nodular cast iron is more difficult to machine than ordinary gray cast iron. Nodular cast iron can suppress vibration and sound better than steel, making it very suitable for large machines.

 

What is the purpose of ductile iron? (Application)

Nodular cast iron is very suitable for occasions where metals with strong wear resistance are required.

The following is a list of examples of items made of or containing ductile iron:

  • Ductile Iron Pipe

  • Axle

  • Connecting rod (such as engine)

  • Crankshaft

  • Cylinder

  • Disc brake caliper

  • Gears and gearboxes

  • Housing and manifold

  • Static bucket

  • Ductile Iron Classical Light Pole Accessory

  • Large machine

  • Mechanical tools

  • Military use

  • Piano harp (the part that holds the piano strings)

  • Spindle support

  • Steering knuckle

  • Suspension system parts

  • Truck axle

  • Valves (especially high pressure valves)

  • Wheel hub

  • Ductile Iron Bench Legs

Ductile cast iron vs cast iron

Cast iron refers to all cast iron parts with high carbon content, but in normal use, "cast iron" refers to gray cast iron, and the castings with weaker cast iron structure contain graphite flakes. Nodular cast iron must have a spherical graphite structure especially in the metal.

Ordinary cast iron can be cast cheaply, is very easy to process, and can increase its strength through heat treatment. Gray iron lacks the strength and durability of ductile iron. The price of ductile iron is not much more expensive than gray cast iron, but if you don't need the benefits of ductile iron, you should stick to gray iron castings.


Προηγούμενος: What Is Ductile Iron Pipe?
Επόμενο: qwedf
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