An Introduction to SG Iron

What is SG Iron?

Majorfax is a Tier 1 supplier and manufacturer of SG Iron (also known as Ductile Iron, Nodular Cast Iron, Spheroidal Graphite Iron and Spheroidal Graphite Cast Iron), which was first created by Keith Millis, invented in 1943. It is a type of cast iron known for its impact, fatigue resistance, elongation and wear resistance due to the spherical graphite structures within the metal, as opposed to the flake structure which can be seen in Grey Iron.

The picture below shows the spherical graphite structures of SG Iron.

Why use SG Iron? 

However, similarly to Grey Iron, there are several grades of SG Iron; each of which offers engineers varying degrees of tensile strength and elongation, giving it a superior strength to weight ratio. This is achieved via a combination of alloy additions and heat treatment. As such, SG Iron has proved to be an effective, lower cost alternative to malleable iron castings, steel forgings and steel fabrications.

Advantages of SG Iron

To summarise, SG Iron offers the following benefits:

  • Tensile strength: The tensile strength of SG Iron exceeds that of Grey Iron, ranging from 400-700 N/mm².
  • Yield strength: SG Iron has a greater yield strength compared to Grey Iron.
  • Weight reduction: SG Iron castings are significantly lighter than steel castings; offering a remarkable strength to weight ratio.
  • High elastic limit and good elongation.
  • Castability: SG Iron has a lower casting temperature to Steel and this allows for a high quality surface finish and the ability to cast complex shapes.
  • Greater impact and fatigue resistance: due to its spherical graphite structure.

SG Iron Applications  

Majorfax manufacturers and supplies SG Iron for a wide range of applications, however below are a list of the more common applications which it is used for.

Pressure Pipes and Fittings

SG Iron has long been used to transport water and other liquids. Its remarkable strength to weight ratio, alongside its toughness makes SG Iron a suitable material to withstand the high operating pressures faced by pressure pipes and fittings.

Agriculture, Road and Construction Applications

The agriculture industry use SG Iron widely for a range of applications; from tractor parts, compressors and brackets, to clamps and pulleys.

General Engineering Applications

The high tensile and yield strength of SG Iron allows it to be a perfect metal to be widely used for all kind of hand tools such as wrenches, clamps, gauges etc.

SG Iron Grades offered by Majorfax

At Majorfax, we manufacture and supply SG Iron in a wide variety of grades (including LT). Listed in the table below are just some of the more popular grades which we offer:

SG Iron Grades



Tensile Strength N/mm

0.2% Proof Stress N/mm2

Elongation (%)

Typical Hardness HB



EN-GJS-400-18(LT & RT)40025018<175400/18

For more information, please contact Ranvir Gill, Sales & Marketing Co-ordinator at Majorfax on

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