Answer: Song economic revolution
Explanation: Iron and steel were put to many uses this uses were from nails and tools, to more heavy chains used for the suspension of bridges and Buddhist statues. The army was a large consumer of this which was used at the tips of their weapons as it helped increased the effectiveness of Song arrows. To achieve this mass production methods were emply to produce iron armor in small, medium, and large sizes, this comprises of high quality steel which were used for swords.