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 parts.
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 grades.
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 necessary.
This article was from Dandong Foundry. For the whole article, please check Dandong Foundry Blog.