Characteristics Of Ductile Iron

Apr. 07, 2022

Cast Iron Pump Bowl

The ductile iron was invented in 1943. It is a group of irons. Due to its microstructure, it exhibits greater flexibility, endurance, and elasticity, and is even more durable than other irons. This iron is considered a modern version of actor iron. Cast iron and ductile iron have different physical properties due to the difference in the microstructure.

Ductile iron has extra flexibility than cast iron because it usually contains more than 3% carbon, so it can be bent, twisted, or defective without breaking. Ductile cast iron has similar properties to steel, which makes ductile cast iron stronger than many standard cast iron.

The main source of ductile iron is pig iron. In addition, ductile iron can also be produced from steel or scrap iron, but pig iron is usually extra, and many modern ductile irons are planned by the store. Pig iron refers to the blast heating system cast by the key antique method for producing pig iron. The iron directly enters the mold organized by the sand bed with more than 90% iron in the blast heating system. These molds and molds make them look like a mess of pigs, so we call these iron pigs.

Today, these little "pigs" are produced in continuous pig casting machines.

Due to its toughness and flexibility, ductile iron is commonly used in many fields. It is commonly used by pipe manufacturers for pipes and fittings. In the automotive industry, it is also very popular because it is used for engine connecting rods, cylindrical tubes, crankshafts, truck shafts, as well as equipment and other components. Similarly, ductile iron is often found in piano harps, equipment frames, and rope drums.

No matter which industry you are in, if you want to find a strong and stable product that can withstand difficult problems for a long time, ductile iron is a good choice.

Definition of irons

A ferrous product classification can be established in terms of the carbon content of the basic metal:

iron : 0 to 0.1% C,

steel : 0.1 to 1.7% C,

cast iron or ductile iron: 1.7 to 5% C

Below 1.7 % carbon, solidification produces an austenitic single phase material, with the carbon present in the structure in solid solution. Above 1.7% carbon, the carbon cannot all be dissolved in the iron structure and consequently solidifies in the form of a secondary phase, either as graphite (pure C), or iron carbide (Fe3C). Iron is a multi-phase material, of complex structure: the most common constituents are ferrite (Feα) and pearlite (Feα + Fe3C). Other elements present in iron in very low proportions have an effect on the structure, mechanical properties and casting of the metal. Silicon (usually 1 to 3 %) plays a particular part and makes the iron in reality, a ternary alloy: iron, carbon, silicon.

Different types of cast iron

The term “Cast iron” covers a wide variety of Fe-C-Si alloys. It is usual to class them in groups according to the graphite condition, making an additional differentiation based on the structure of the metal matrix (ferritic, pearlitic).

Effect of graphite shape

In so-called “grey irons” the graphite is present in the form of flakes, hence their metallurgical name: flake graphite irons (sometimes called lamellar graphite irons). By concentrating abnormal stresses at certain points, each of these flakes may initiate cracking.

Metallurgists have therefore sought to diminish, or eliminate, this effect by changing the size or distribution of the flakes. In a first stage, the adoption of the centrifugal process to cast flake graphite iron pipes (so-called “grey iron pipes”), led to an appreciable improvement, by producing very fine graphite flakes. A decisive advance was then made in 1948 when research in both the U.S.A. and Great Britain led to the discovery of spheroidal graphite iron, more commonly known as ductile iron.

The graphite no longer exists in flake form but precipitates in a spherical form. The possibility of crack propagation lines is therefore eliminated. Graphite precipitation in spheroidal form is obtained by the controlled addition of a small amount of magnesium to the previously desulfurized base iron.

Characteristics of Ductile Iron

Ductile iron owes its remarkable mechanical properties to the spheroidal shape of its graphite:

  • tensile strength,

  • impact resistance,

  • high elastic limit,

  • good elongation.

These properties are further enhanced by control of the chemical analysis and heat treatment of the metal matrix.

Ductile iron maintains the traditional qualities of cast irons, resulting from the high carbon content:

  • compression strength,

  • castability,

  • abrasion resistance,

  • machinability,

  • fatigue strength.

To develop different grades of ductile iron, the matrix framework around the graphite should be adjusted during the laying process or through subsequent heat treatment. There are slight differences in composition between different grades of ductile iron to produce the required matrix (microstructure).

Nodular cast iron can be regarded as steel with graphite balls dispersed in the matrix. The quality of the metal matrix suspended by the graphite balls has a substantial effect on the performance of ductile iron, however, the graphite spheroids themselves have no effect.

Many matrices are found in ductile iron, the most typical of which is ductile iron.

Ferrite-a pure, ductile, low-strength adaptive iron. The matrix has insufficient wear resistance but has high effective wear resistance and excellent machinability.

Pearlite-a mechanical mixture of ferrite and iron carbide (Fe3C). It is relatively hard and has moderate ductility. It has high endurance, good wear resistance, moderate anti-effect, and good machinability.

Pearlite/ferrite-a structure composed of pearlite and ferrite, and one of the most common matrices in industrial ductile iron.

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