WI:A Roman Blast furnaces

[General_Finley]

At first I was going to ask about what the impact of the slow evolution of gunpowder in Europe would have been had it been discovered in the 5th century in the ERE; just as I was about to post the question I was like "What if the Romans invented paper?" and was ready to open up a thread on the impact on Europe if the Eastern Romans did in the 5th or 6th century what Cai Lun did in the 2nd. I started to look up Chinese inventions and increasingly wondered what would be the impact on Europe if many of them had been independently invented, and then I came across the Blast furnace. So my question is what would be the impact on the Roman world if the Blast Furnace had been independently invented by the Romans in the 5th century?