No. The only way to increase the threat range of a bludgeoning weapon is either through Improved Critical or the Powerstrike option of the Runeforger ability from the Forgemaster dwarven cleric archetype.
Was one in 3.5, none in pathfinder I know of.
Hey I don't know if I was high or just cant remember what it is called!
but what is the spell name for a spell that increase the threat range of a hammer or other bludgeoning weapon?
No. The only way to increase the threat range of a bludgeoning weapon is either through Improved Critical or the Powerstrike option of the Runeforger ability from the Forgemaster dwarven cleric archetype.
Or, alternatively, yes, there are several ways, one of which is a spell.
There's the Wrath spell, for Inquisitors.
Or the Knights Candidate achievement feat.
Or the Skirmishers hunter trick Hateful Attack.
Or the Cavalier ability Mighty Charge.
Or the Slayers Knack feat.