Does March of the Machines make artifacts in hand creatures as well?
On any given card, a card that specifies a permanent type without explicitly saying 'card' only affects permanents in play (unless otherwise specified by the card).  If you have an artifact card in your hand, it is exactly that - an artifact card, and not an 'artifact'... 

Relevant rule


  109.2. If a spell or ability uses a description of an object that includes a card type or subtype, but doesn’t include the word “card,” “spell,” “source,” or “scheme,” it means a permanent of that card type or subtype on the battlefield.


(https://mtg.gamepedia.com/Object)