Norse helmets were made of metal or leather and had no horns on them. Only rich people could afford helms, as with any armour, in the first place.
Horned helms are depicted on some picture stones from the early iron age. That doesn't mean that people wore them, though. It could mean that the depiction is of a specific god that is closely associated with this (a code we no longer know how to understand), or it could be something that someone wore during ritual, such as a shaman. Both things are done in many non-judeo-christian religions today. As archaeologists we find many things that look like weapons or armour but that serve no functional purpose (such as battleaxes made to look like stone, but that are actually made of clay, and so cannot cut, or weapons that look like metal but are actually made from stone, since people had seen them used in ritual and wanted to use such things themselves in their own ritual, but before they had learned to extract the metal itself). They have generally been used for ritual purposes, to represent a god or goddess, we think.
