Underwater Societies could use Hydrothermal Vents to make the metal hot enough to form into some parts, or they could find magma and use it to smelt metal. Smelting does not necessairly need FIRE, smelting only needs HEAT, which is why Underwater Societies could use Hydrothermal Vents and Magma. It would be harder to smelt metals with higher melting temperature, tho, but still they can melt SOME metals, which is enough to make some suit for exploring the Surface, then you could use those to melt other metals on the surface, and industrial age is then guaranteed. Any reasons now why Underwater Civs would not reach space?
Aside from the fact that they would need ridiculous heat resistance to be able to be close enough to the vents to melt metal without melting themselves? Water is a lot better at conducting heat than air is.
Water is cold… you know? So creatures are able to survive some time near heat vents, along with heat vents sending heat UP.
Yeah, but they need to be able to be close enough that the metal they’re interacting with will melt. And the person in question will probably boil long before they get that close. Water near heat vents isn’t cold at all. Water conducts heat better over distance than air does, so while in air being a few meters away from the point at which the metal is melting might be enough, under water it’s not going to be.
There is a lot of variants how they can safely smelt stuff, or rather, get them red hot to form them into stuff, first of all, Rock Tools to hold Red Hot Metal! With that they could form it by using chiseled stone for shapes and parts (definetly gears or casings), it would become easier after specific devices are made, or, of course they could risk some people to build a furnace around a Hydrothermal Vent, there is never actually a possibility that the aquatic creature has resistance to heat!
Please, just read this thread:
Besides, they couldnt develop advanced enough tech because every circuit they make would be fried by the water