Is the cheating effect on this too strong? Should it only hit graveyards? Is that too weak?

I think the flavor and balance would be better if it only hit graveyards.

I think this is pretty weak if it only hits graveyards.

Missing the "W" on "Whenever".

One problem with the current wording is that if Sword of Forge and Furnace is the only artifact on the battlefield, you either destroy it or the artifact it's returning. "Cheating" artifacts into play may not be necessary, since if you swing you might have an open board of lands to cast that artifact you're returning. My suggested wording, based on the wording/power level of Sword of Light and Shadow:

"Whenever equipped creature deals combat damage to a player, you may destroy target artifact and you may return up to one target artifact card from your graveyard to your hand."

We gave this sword's triggers a bit of extra oomph. Protection from Artifacts is far weaker than the protection from two colors other swords give. Since this sword leaves its wielder much more vulnerable, as well as easier to block, the hit triggers could be stronger than others. This is especially true since the sword is only really good in an artifact deck while other swords are essentially universally good. I think adding "may" to the destruction clause is a good idea though.