Ductile iron--what is it?

Question

On the wheeloaders (payloaders) we build at the plant I work at, one of the main lift arms has the words 'ductile iron, do not weld', embossed on it.
Oddly enough one of the engineers at the plant could not answer my question. What is 'ductile iron' and why can it not be welded?

Answer 1

Ductile iron is any one of several cast iron alloys formulated and processed to eliminate the brittleness of common cast iron. The properties of this iron depend on specific heat treatment. The weld joint will have a very different thermal history from the rest of the material, and will be weaker and more brittle than the rest of the structure.

Answer 2

Ductile Iron also known as SG Iron (Spheroidal Graphite Iron). This is a special type of Cast Iron, where the carbon in the alloy is in the form of Graphite in spherical shape. This increases the ductility of Cast Iron (As you may know generally Cast Iron is very brittle). But, this is still cast iron, and cast iron cannot be welded due to the presence of excessive carbon (> 2%).

Answer 3

ductile iron is just iron that is less brittle and more managable than other types of iron. The iron is too soft to weld