Iron has been mentioned before in the context of the sample of 25 embedded objects. Dutch chief prosecutor Fred Westerbeke described the samples as 25 pieces of iron. At that time (Sept. 12) he was investigating whether the pieces came from a ground to air missile.
It wasn't reported whether any of the other 475 embedded objects contained iron. It wasn't reported whether they also examined all foreign objects for metals other than iron, such as tungsten, that are hard and dense enough for military application as penetrators.
The comfortable assumption is that the investigators are professionals who of course are interested in any and every foreign object that could have penetrated the aircraft. Perhaps they will say so eventually, but so far they haven't.