ASTM A536 70-50-05 is a high grade of ductile iron according to the American standard.
The yield strength of ductile cast iron 70-50-05 is no less than 345MPa, the tensile strength is no less than 485MPa, and the elongation (L0=50mm tensile test bar) is no less than 5%. It is equivalent to ISO grade 500-7, China QT500-7, Germany GGG50, EN-GJS-500-7, UK 500/7, Australia 500-7.
This grade of ductile iron is suitable for special applications, such as pipes, fittings etc. In practice, Grade 80-55-06 is better than this grade. Therefore, many clients will use 80-55-06 ductile cast iron instead.
Standard ASTM A536 has no requirement to the chemical composition. Hence the iron foundry could adjust the chemical composition according to their experience. However, the mechanical properties are the necessary requirement.
This material grade has high tensile strength, but the elongation is not high. That means it is strong, but does not have good ductility. Therefore, unless you have special reasons, otherwise, the equal grade 80-55-06 may be a better choice.
The following is the mechanical requirement to this grade.