Spheroidal cast iron (EN-GJS) or spheroidal graphite cast iron?
These two terms are descriptions for the same kind of cast iron. The term spheroidal derived from Greek and also means sphere. Spheroidal cast iron is a further development of grey cast iron (EN-GJL). Due to the high carbon content, grey cast iron has significantly better and more efficient casting properties than steel. On the other hand, and as a result of that, grey cast iron is very brittle and not weldable. Therefore, a way was sought for bringing together the good casting properties of grey cast iron and the better elongation and tensile strength of steel in one cast material – the spheroidal cast iron.
Spheroidal cast iron – the sphere as ideal shape
It has long been recognized that the brittleness of grey cast iron is a result of the flat and slat-like deposits of carbon. The large and flat slats create a reduction of the cohesion, hence a reduction of the connection strength between the molecules, so that they act like a separation between the iron crystals. What’s more is the notch effect, which is created by stringing together the slats. A crack in a grey cast iron body is therefore mainly following the carbon graphite slat chains. Accordingly, a way had to be found to get an ideal form of the graphite – the spherical shape. Thanks to the spherical shape, all disadvantages of the previous notch effect are eliminated in spheroidal cast iron. Under tensile or elongation stress, the forces are directly redirected around the shape of spheroidal cast iron. In a similar way, the cohesion will substantially be improved. The result of this process would be a cast part of spheroidal cast iron, with the advantages of grey cast iron and also, to a great extent, of steel.
From initial successes to the ideal cast iron
Already in the 1930th, the first with spheroidal cast iron with graphite was produced in Germany, but it wasn‘t until the 40th that the US were successful in starting a rational and industrial production of spheroidal cast iron through the treatment of the iron melt with magnesium and nickel. However, the major breakthrough has been made possible through another German development by adding an alloy of ferrosilicium and magnesium to the melt. This was followed by further treatment procedures with individual advantages. Spheroidal cast iron in its present quality features a high elongation at high tensile strength and cast quality, which made it possible to achieve the goal to create an economically favorable alternative to steel.
Spheroidal cast iron (EN-GJS) in its diversity
The term GJS translated stands for cast-iron-spherical. The former term GGG (globular grey cast) was ceased. Today, spheroidal cast iron, GJS, is available in many different qualities, which are achieved by combining different alloy components. Hence, the carbon content differs between 3.4 % and 3.8 %. Additionally, there is in spheroidal cast iron a silicon content of 2 % to 3 % as well as small amounts of precious metals of approx. 1 %. These include, inter alia, manganese, chromium and copper. Sulphur is used in spheroidal cast iron in a very small amount of just 0.003 to 0.015 %. Even though a corrosion resistance was not specified as a certain target, it came up automatically to a great extent, regarding the necessary alloy components.
Ready-to-assemble parts of spheroidal cast iron
The Silbitz Group does not only produce cast parts made of spheroidal cast iron in different qualities, but already starts to develop an optimal workpiece of spheroidal cast iron during the construction, taking into account the casting-related design. The requirements of the customer are considered in direct cooperation. Thanks to subsequent machining, using most modern machining centres, the customer receives ready-to-assemble parts of the highest quality and precision. It is also possible to develop special qualities in cooperation with the customer, whereby the weight can differ between 10 kilos and 45 tons. Due to its excellent features and all its various compositions, spheroidal cast iron has been accepted as an important material for cast parts during the last few decades. Today, the more efficient spheroidal cast iron has proven itself to be the better alternative to steel, welded and forged parts in all our sectors.