It would take substantially less energy to make metal molten in space. As air pressure drops, the temperature needed for materials to change states becomes lower. That’s why water boils much faster on a mountaintop than it does at sea level.
The metal would be manually workable at relatively low temperatures. Without air, you would need a tank of a gaseous substance to “blow” into the metal.
While it’s true that the relationship between melting point and boiling point differ from material to material, the melting point always remains below the boiling point until the triple point.
The triple point is when the ambient pressure is low enough that a substance can be solid, liquid, and vapor in equilibrium at the same time.
As for engines, they burn at temperatures hot enough to melt the steel they are made of, even while on Earth. Engineers employ regenerative cooling to prevent the housing from melting at such high temperatures.