ASTM A536 grade 70-50-05 is a high grade of ductile iron. It is a ductile iron material grade used in USA, also equal to ISO grade 500-7, China QT500-7, Germany GGG50, EN-GJS-500-7, UK 500/7, Australia 500-7.
According to the standard of ASTM A536, this material grade requires Tensile Strength min. 485 MPa, Yield Strength min. 345 MPa, Elongation min. 5%.
This material grade is the ductile iron used for special applications, such as pipes, fittings etc. Actually, Grade 80-55-06 is better than this grade, so many clients are using grade 80-55-06 as replacement.
In standard ASTM A536, there is no requirement to the chemical composition, so the iron foundry could adjust their chemical composition as their experience, but the mechanical properties as above are the necessary requirement.
This material grade has high tensile strength, but the elongation is not high, so it is strong, but does not have good ductility, so 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.