Ductility: Definition, Meaning & Factors that Affect

What is Ductility?

Ductility is when a solid material stretches under tensile strain. If ductile, a material may be stretched into a wire. Malleability, a similar property, is a material’s ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.

Both of these properties are aspects of plasticity. Plasticity is how far a solid material can be deformed without fracture. These properties are commonplace in metals and are dependent on temperature and pressure. This was investigated by Percy Williams Bridgman as part of his 1946 Nobel Prize-winning work on high pressures.

Ductility and malleability do not always go together. Gold has high ductility and malleability, but lead has low ductility and high malleability. The word ductility is sometimes used to embrace both types of plasticity.

Examples: Most metals are good examples of ductile materials, including gold, silver, copper, erbium, terbium, samarium aluminum, and steel have high ductility. Examples of metals that are not very ductile include tungsten and high-carbon steel. Nonmetals are not generally ductile.

Definition of Ductility

Ductility is the ability of a material to be drawn or plastically deformed without fracture. It is therefore an indication of how ‘soft’ or malleable the material is. The ductility of steel varies depending on the types and levels of alloying elements present. An increase in carbon, for example, will increase the strength but decrease the ductility.

Ductility Meaning

Ductility is a mechanical property commonly described as a material’s amenability to drawing (e.g., into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stress before failure.

Ductility is an important consideration in engineering and manufacturing, defining a material’s suitability for certain manufacturing operations (such as cold working) and its capacity to absorb mechanical overload.

Ductility is measured by the strain suffered by the material before fracture. In a tensile test, it may be measured by percent elongation in engineering terms, or by logarithmic strain at the fracture point. In compression tests, similar measures may be used. In the torsion test, it is measured by the strain suffered by an outer layer of material of the test bar before fracture.

The tensile tests show low ductility because of neck formation and consequently, the negative hydrostatic pressure in the neck region promotes crack initiation and propagation. This problem is not there in compression and torsion tests which show higher ductility for the same material. Many researchers have preferred the torsion test for the measurement of ductility while the strength properties are related to those measured in a tensile test.

Ductility
Ductility

Factors that Affect Ductility of Metals:

Ductility is affected by intrinsic factors like composition, grain size, cell structure etc., as well as by external factors like hydrostatic pressure, temperature, plastic deformation already suffered etc.

Some important observations about ductility are given below:

  1. Metals with FCC and BCC crystal structure show higher ductility at high temperatures compared to those with HCP crystal structure.
  2. Grain size has a significant influence on ductility. Many alloys show super-plastic behavior when the grain size is very small in the order of few microns.
  3. Steels with higher oxygen content show low ductility.
  4. In some alloy’s impurities even in very small percentages have a significant effect on ductility. The ductility of carbon steels containing sulfur impurity as small as 0.018%, drastically decreases ductility at around 1040°C. This can however be remedied if Mn content is high. In fact, the ratio Mn/S is the factor that can alter the ductility of carbon steels at 1040°C. With the value of this ratio at 2, the percent elongation is only 12-15% at 1040°C while with a ratio of 14 it is 110 percent.
  5. Temperature is a major factor that influences ductility and hence formability. In general, it increases ductility, however, ductility may decrease at certain temperatures due to phase transformation and microstructural changes brought about by an increase in temperature. The effect of temperature on the ductility of stainless steel. It has low ductility at 1050°C and a maximum at 1350°C. Therefore, it has a very narrow hot working range.
  6. Hydrostatic pressure increases ductility. This observation was first made by Bridgeman. In torsion tests, the length of the specimen decreases with an increase in torsion. If the specimen is subjected to axial compressive stress in the torsion test it shows higher ductility than when there is no axial stress. If tensile axial stress is applied the ductility decreases still further.

FAQs.

What Is Ductility?

Ductility is when a solid material stretches under a tensile strain. If ductile, a material may be stretched into a wire. Malleability, a similar property, is a material’s ability to deform under pressure (compressive stress). If malleable, a material may be flattened by hammering or rolling.

What Is Definition Of Ductility?

Ductility is the ability of a material to be drawn or plastically deformed without fracture. It is therefore an indication of how ‘soft’ or malleable the material is. The ductility of steel varies depending on the types and levels of alloying elements present. An increase in carbon, for example, will increase the strength but decrease the ductility.

What Are The Example Of Ductility?

Examples: Most metals are good examples of ductile materials, including gold, silver, copper, erbium, terbium, samarium aluminum, and steel have high ductility. Examples of metals that are not very ductile include tungsten and high-carbon steel. Nonmetals are not generally ductile.

What Is the Meaning Of Ductility?

Ductility is a mechanical property commonly described as a material’s amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stress before failure.