Nodulizing Grades of Ductile Iron
Nodulizing grades are also called as
nodularity grades, nodularization grades, or percent of
spheroidization. It is a very important standard to evaluation the
quality of ductile iron microstructure. High nodulizing grade means
the high quality and better mechanical properties of iron casting
Nodulizing levels have five grades, the grade 1 is the best, and the
grade 5 is the worst. The following is the detail description to all
Percent of spheroidization is upper than 95%. The most of graphite
is spherical, and has very few floccules. This requirement is the
highest for the microstructure. Normally, only the iron castings
used for automotive industries especially for small cars will
require so high nodulaizing grade. Therefore, most of iron foundries
could not meet this requirements, expect for the professional iron
foundries for automotive industries.
Percent of spheroidization is between 90% and 95%. Most of graphite
are spherical and have few floccules. This grade is also very high,
normally this requirement is applied to the key iron castings used
for heavy and engineering vehicles such as trucks and tractors. Only
good iron foundries could meet this grade.
Percent of spheroidization is between 80% and 90%. Most of graphite
are blob-like, have some floccules, and very few vermiculate. This
grade is common for most of important iron casting parts. Most of
iron foundries in China could meet his requirements. However, this
grade is not low, the iron foundries should use the good materials
to reach this grade.
Percent of spheroidization is between 70% and 80%. The graphite are
mixed by the spherical, blob-like, floccules and vermiculate.
Normally, lower than 75% is not qualified for ductile iron.
Percent of spheroidization is between 60% and 70%. The graphite are
mixed by blob-like, floccules, vermiculate and lamellate. Of course,
this grade is very low, but you could not say that it does not meet
the requirements of ductile iron. If your designer just required the tensile
strength and elongation to the ductile iron, then the inspection to nodulizing
grades will not be necessary. In other words, nodulizing grades are just the detail requirements to the
microstructures of ductile iron castings.
Nodulizing grade is inspected by the
metallographic microscopes. Most of large iron foundries in
China have this device in-house. So, as buyers, you could ask your
suppliers to do this inspection if your designers think this is