|Original "First Iron Brigade" Medal . circa January 1863|
"There was another organization, in the Army of the Potomac, known as the Iron Brigade, and it was in the same division with the "Iron Brigade of the West." It was composed of the Second United States Sharpshooters, the Twenty-second, Twenty-fourth, Thirtieth, and Eighty-fourth New York (14th Brooklyn), forming Hatch's (1st) Brigade, First Division, First Corps.
But the Twenty-second, Twenty-fourth, and Thirtieth New York were two years regiments, and were mustered out in May, 1863, thereby breaking up the organization. The Eighty-fourth New York (14th Brooklyn) was an exceptionally fine regiment, while the other regiments in the brigade made a reputation, also, as efficient commands.
It seems strange that two brigades in the same division should adopt like synonyms; but, in justice to Hatch's Brigade, it should be stated that it was the original Iron Brigade, and that Gibbon's Brigade was not known by that title until after Antietam, at which time it was so designated by a war correspondent, who was apparently unaware of his lack of originality."
Find more here : Fox's Regimental Losses 1861 - 1865