I've been researching Chinese blast furnaces and cast iron. Frankly most of the science is way over my head but I've been able to make out the gist of it so far, if only slightly.
Anyways, I came upon this site which basically refutes the argument that China was any more advanced than the West in metallurgy. I know that it seems kind of politically or ideologically motivated, but the scientific arguments seem sound, at least to someone like me who does not have a background in metallurgical sciences. I would like to see what more knowledgeable people have to say about the following statements:
The early Chinese techniques included a kind of puddling" process, which is similar to processes used in the West much later (let's say after 1500 AD). Does that mean that the Chinese were 1000 years or so ahead of the West? It's a matter if definition. If you prefer a bad steel made by an advanced method to good steel made in an old-fashioned way, the Chinese were ahead.
The Chinese cast-iron industry certainly pre-dates "ours" by 1 500 years or so. The reason, however, is not that the Romans or others in the West couldn't make cast iron! They could, in fact, but they didn't want to! They simply had no use for the brittle stuff. The Chinese, to their everlasting credit, used their cast iron for making peaceful objects, including flower vases and (huge) sculptures. Western cast iron, when it was finally produced, went immediately into cannon making.
So basically, did the Chinese use an advanced method to produce bad steel while the West used an older method to produce better steel? Did the Romans have blast furnaces, but had no use for cast iron, while the Chinese found cast iron more useful than the rest of the world?
For most purposes, cast iron (carbon content usually 3.5-4%) is inferior to steel (carbon content of up to 2%) or wrought iron (low carbon content, too low to harden). As said on that page, it's brittle.
But it was relatively cheap. The Chinese did convert cast iron to steel (by decarburising), but this added additional fuel and labour costs. After converting it to steel, the final object still needs to be made, by forging - more fuel and labour costs. If brittleness was acceptable, the desired object could be cast straight from the smelter, cutting out those additional costs.
So, for Chinese iron and steel after the widespread adoption of the blast furnace in China, the cheap end of the market was dominated by cast tools, and the high end of the market was dominated by forged wrought iron and steel tools and weapons. Weapons, where brittleness is quite undesirable (nobody likes it when their sword blade breaks in battle), were forged steel.
(Cast iron can be the best choice for ploughshares/plowshares, since it has high wear resistance.)
So yes, the Chinese did deliberately make many of their iron/steel objects out of an inferior alloy (cast iron), but they did so for the very sensible reason that it was cheaper. Where a better alloy (steel) was needed, they converted the cast iron to steel, and made the tool/weapon/object by forging.
It is possible to produce cast iron in a bloomery furnace, especially in a blast-bloomery (a bloomery furnace with a forced draught). But it's usually considered undesirable, an unwanted waste product. The Chinese blast furnace was not just a blast-bloomery, though, but continuously-fed and continuously tapped. Traditional blast furnaces were still being used in China into the 20th century; they were capable of being run continuously for about 40 days, with significant efficiency advantages over a bloomery or blast-bloomery (modern blast furnaces often operate continuously for 40 weeks). This difference in furnace types means that even if the Romans had deliberately made cast iron and cast it into objects, they would have been more expensive, relative to Chinese cast iron.
While the Chinese did have what could be considered very advanced metallurgy, a lot of nonsense is written about it. Advanced, but not magic. Föll is quite correct with his comments on such nonsense on that page. Perhaps "bad steel made by an advanced method" is a poor choice of words, since cast iron is, by the most common definitions, not steel, and thus cast iron cannot be "bad steel", but he is quite correct to point out that much of the output of the advanced Chinese iron industry was objectively inferior cast iron objects.
And, of course, "much of the output" is not "all of the output". While cheap cast iron was an option, the Chinese also made (by forging) objects of high quality steel.
For more on Chinese iron and steel, see Donald B. Wagner, Iron and Steel in Ancient China, Brill (1996) and Science and Civilisation in China, Vol. 5, Part 11, "Ferrous Metallurgy" (also by Donald B. Wagner) (2008).