It's my understanding that early civilizations were limited to using copper and the alloy bronze due to their inability to produce enough heat to melt iron. Once they were able to do this, the iron age started, since iron was easier to acquire than bronze, and a long time after that steel became commonly used, being superior to iron.
What are the factors that go into kilns and furnaces that prevented early peoples from working with iron and steel? What technological or design advancements were made that allowed people to heat metals to higher temperatures? Why couldn't a bronze-age civilization make a furnace hot enough to smelt iron and forge it into steel?
What are the factors that go into kilns and furnaces that prevented early peoples from working with iron and steel? What technological or design advancements were made that allowed people to heat metals to higher temperatures?
All that's really needed to reach higher temperatures is better airflow for the fire. There is the question of why one would bother, since a hotter furnace is usually more fuel-hungry, and can be more likely to make pottery being fired in a kiln explode. More specifically, until you reach stoneware firing temperatures, a little bit hotter still only gives you earthenware pottery, with more expense and more chance of failure.
Why couldn't a bronze-age civilization make a furnace hot enough to smelt iron and forge it into steel?
No reason why they can't, and in fact they did. It's just that once furnaces hot enough for iron smelting are common, the civilisation usually enters the Iron Age.
their inability to produce enough heat to melt iron
Being able to melt iron typically came much later than iron smelting ("smelting" = turning ore into metal). The temperatures needed for iron smelting are well below the melting point of iron.
Similar questions have been asked before. See the answers by myself and u/rocketsocks and u/Antiquarianism and [deleted] in