As known to experts in the area, the vermicular cast iron comprises a group of Fe-C-Si alloys and also contains Mn, P, S, with controlled additions of Mg, presenting graphite predominately in vermicular form (form IV according to Standard ASTM A247), with up to 20% of nodules (forms I and II Standard ASTM A247) in its microstructure.

To obtain the desired class of that iron alloy, its ultimate tensile strength may be changed from 350 to 500 Mega Pascal through complementary additions of pearlitic elements such as Mn, Cr, Cu and Sn.

The vermicular cast iron has been increasingly applied in automotive components such as internal combustion engine blocks, internal combustion engine heads, disks and brake drums.

When applied to automotive components, additions of Ti may be done to increase the resistance to wear out and to improve the lubrication of the cylinder in engine blocks.

To be applied in components of the automotive line, the substitution of gray cast iron by vermicular cast iron is usually done to increase the tensile strength of the said components. This substitution, however, brings some

manufacturing problems not yet entirely solved.

One of these problems is the low machinability of the vermicular cast iron when compared to the gray cast iron.

The low machinability of conventional vermicular cast iron is a characteristic known to the material which reflects in the decrease of a tool life when compared to the machining of gray cast iron.

The decrease in the tool or component life is real and effective, being its quantitative parameter dependent on the machining operation in particular. It can be observed that such reduction is of at least 50% in milling and boring operations, and could decrease up to 95% the life of the tool in cylinder hole reaming operations.

One of the goals of the present invention is to provide vermicular cast iron of high machinability, that allows an increase in the life of tools to be used with the cast part together with the innovated characteristics.

Another goal of the present invention is to provide vermicular cast iron of high machinability that presents a machinability at least 40% bigger than the conventional vermicular cast iron, machinability evaluated by the life of the cutting tool.

This and other goals and advantages of the present invention are achieved with vermicular cast iron of high machinability that comprises the inclusion of a defined amount of graphite in its microstructure and in the limitation of harmful chemical elements, besides defining

the parameters for the correct pearlite interlamellar spacing.

With the definition of the correct amount of graphite in the vermicular cast iron, it is possible to incorporate an important microstructural aspect as the graphite acts as a lubricant to the cutting tool, thus maximizing its life.

While the amount of graphite varies from 8 to 11% (in volume) in the conventional vermicular cast iron, in the vermicular cast iron of high machinability, object of this invention, the ideal amount of graphite in the microstructure is between 10 and 13%.

This range of graphite percentage quantification is obtained through the adequate dimensioning of the contents of Carbon and Silicon, which shall be between 3,5 and 3, 8% for C and between 2,0 and 2, 6% for Si.

An even better improvement in the machinability of the vermicular cast iron is obtained, if compared to the conventional vermicular iron, when elements that form carbide or carbonitrides (Cr, Mn, Ti) are limited.

With the limitation of the content of Chromium to a maximum of 0, 050%, of the content of Manganese to a maximum of 0, 40% and of the content of Titanium to a maximum of 0, 015%, it is possible to obtain an effective machinability of the component or part conceived by the vermicular cast iron. It is important to mention that those limitations are only achieved, in practice, with the use of metallic raw materials of high purity.

In addition, the machinability of the vermicular cast iron is improved with the formation of pearlite of lamellar spacing bigger than 0,5 microns, which is obtained under controlled conditions of part cooling at a temperature ranging between 800° and 650°C.

The machinability advantages previously mentioned are thus increased.

Despite the fact that a preferred constructive concept has been described and illustrated, it is important to mention that changes are feasible and possible to be carried out without deviating from the scope of the present invention.