With modern knowledge, what would be the most effective way to smelt iron with bronze age technology?

Question

Basically, assuming you have all of modern human knowledge about smelting iron/steel, and the technology level you have is approximately bronze age, what would be the most effective approach to turn iron ores into usable iron tools? Specifically, the approach that would result in the highest quality result, as well as be as easy as possible to do at a large scale (if these don't conflict).

You can assume the technology available includes clay or adobe bricks, pottery, copper and bronze tools, and anything else a later bronze age civilization could be expected to have, in addition to whatever knowledge is needed for the process (this is handwaved, there doesn't need to be a plausible reason they'd know how to do it).

From what I've read, bloomery furnaces with charcoal as fuel were almost always the first ones to be used when civilizations entered the iron age. However, since we now know about all sorts of methods of making iron and steel, I'm wondering if that knowledge could be exploited without today's existing infrastructure. For example, using coke instead of charcoal, or preheating the air used in the furnace, or even using a blast furnace immediately instead of starting out with bloomery furnaces.

I'm not too knowledgeable about this sort of thing, but it's important for a story I'm writing. Any ideas?

Answer 1

IIRC China went to blast furnaces with waterwheels and windmills to power bellows very, very early. I don't know much about metallurgy but I do know ceramics, and their high-T furnaces were hollowed out earth mounds or hillsides that generated really powerful draughts as well as having excellent efficiency and top temperatures. They were able to produce tens of thousands of items at a time in medieval times, something only matched by the Europeans in the late 19th century.

The Europeans basically only reinvented porcelain with solar furnaces using big lenses, and then had to figure out how to make furnaces for actual production. I expect the layout and scaling-up of your steelmaking facility will be important and I'd look to China for how you'd do it with premodern technology.

If a very limited amount of steel is all you need, e.g. for demonstration purposes, there's also the possibility of asking the locals about if they know of any places with crashed meteorites....

Answer 2

If a civilization has all the tech you mention and the knowledge of how to make iron they are already ready to start their iron age.

Bronze tools and charcoal fires are more than enough to begin the production of your first iron tools.

First step would probably be bloomery furnaces which can easily be made from mud bricks. The civ would take iron ore and begin attempting to smelt it (different from melting, smelting gets the iron into a semi liquid like state where impurities melt and burn away and the iron begins to slowly meld into a bloblike mass called a bloom).

Assuming a bloom forms (sometimes it doesnt a multiple attempts with more and more iron ore are required to get a good bloom) they would then need to extract it, ideally with long bronze tongs (they can handle a brief moment in the heat though water should be kept nearby so you can occasionally cool of the tongs as needed).

Once extracted they should place it on an anvil of any kind (a log, flat stone, or bronze anvil will work fine at this stage). Then they should begin hammering it like crazy. Between 3 and 5 men with bronze hammers can easily consolidate the bloom into a mostly solid block and then flatten that block into bars. From there you can make any iron tool you desire without too much trouble.

Of course its easier to say this than to do it but the biggest obstacle for the bronze age civilization is just knowing all the little tricks and techniques needed to make iron, not their tech itself (oh and getting a good bloom, depending on your ore, this can be a hard part).

Furnaces that melt bronze can be used to smelt iron either as is or with minor adjustment, smiths who work with bronze will need to get used to smithing as opposed to casting but its not so different from working copper while its cold.

If you need to progress further your second and much harder step would be to make a blast furnace to fully melt large quantities of iron. This allows for more pure iron and steel but takes much more work to get smithable bars (as the bars you get from a blast furnace tend to be too high in carbon content for smithing so you have to lower the carbon content by heating them and then annealing them in cycles).

That being said bloomery furnaces produce a small amount of steel every time they make a bloom, if you know what to look for you can extract small bits of steel from a bloom and eventually get enough to make an entire bar of high carbon steel.

Answer 3

Make a hot blast furnace leveraging the skill of local copper and meteoric iron smiths

The big difference between a bloomery kiln and a hot blast furnace is the copper piping used to pre-heat the air before you blow it into the furnace... and if you are in the bronze age, you are surrounded by skilled copper smiths capable of making such piping. Everything else can be made from mud, stone, and softened leather.

The biggest shortcoming you will have is that you will not be able to precisely measure the temperature and cooling rate of the metals you are working with for proper tempering, but luckying for you, the bronze age had iron smiths who already know how tempor by sight. There is evidence of tempered meteoric steel going all the way back to the beginning of the bronze age; so, all you need to do is find such an iron worker and get him working with your mass produced iron instead of his rarer more expensive meteoric iron.

Lastly, there is magnesium oxide. Magnesium oxide is pretty common in Greece and Asia Minor and can be added to iron to significantly improve the quality of steel compared to a pure carbon steel. Depending on where you go back to, you may need to work a bit hard to bring magnesium oxide to your iron smiths or vice versa, but if you can, then you'll not just be able to recreate the quantity of an industrial era steel mill, but also the quality. Many bronze age Empires were large and organized enough that they should be able to support an industrial revolution if the technology were introduced.

Answer 4

Polished bronze shields, bundling sun into one hotspot furnace in the center of a valley driving up the temperatur of the ore would be my solution. The ore is either https://en.wikipedia.org/wiki/Bog_iron or something you gained via electro-chemistry, because you can totally build a copper dynamo and use the galvanic properties.

Its lame, its not really practical but its doable.