text: Historians debate whether bloomery-based ironworking ever spread to China from the Middle East. One theory suggests that metallurgy was introduced through Central Asia. In 2008, two iron fragments were excavated at the Mogou site, in Gansu. They have been dated to the 14th century BC, belonging to the period of Siwa culture, suggesting an independent Chinese origin. One of the fragments was made of bloomery iron rather than meteoritic iron.
  The earliest iron artifacts made from bloomeries in China date to end of the 9th century BC. Cast iron was used in ancient China for warfare, agriculture and architecture. Around 500 BC, metalworkers in the southern state of Wu achieved a temperature of 1130 °C.  At this temperature, iron combines with 4.3% carbon and melts. The liquid iron can be cast into molds, a method far less laborious than individually forging each piece of iron from a bloom.
  Cast iron is rather brittle and unsuitable for striking implements. It can be decarburized to steel or wrought iron by heating it in air for several days. In China, these iron working methods spread northward, and by 300 BC, iron was the material of choice throughout China for most tools and weapons. A mass grave in Hebei province, dated to the early 3rd century BC, contains several soldiers buried with their weapons and other equipment. The artifacts recovered from this grave are variously made of wrought iron, cast iron, malleabilized cast iron, and quench-hardened steel, with only a few, probably ornamental, bronze weapons.
  During the Han Dynasty (202 BC–220 AD), the government established ironworking as a state monopoly, repealed during the latter half of the dynasty and returned to private entrepreneurship, and built a series of large blast furnaces in Henan province, each capable of producing several tons of iron per day. By this time, Chinese metallurgists had discovered how to fine molten pig iron, stirring it in the open air until it lost its carbon and could be hammered (wrought). In modern Mandarin-Chinese, this process is now called chao, literally stir frying. Pig iron is known as raw iron, while wrought iron is known as cooked iron. By the 1st century BC, Chinese metallurgists had found that wrought iron and cast iron could be melted together to yield an alloy of intermediate carbon content, that is, steel.
  According to legend, the sword of Liu Bang, the first Han emperor, was made in this fashion. Some texts of the era mention "harmonizing the hard and the soft" in the context of ironworking; the phrase may refer to this process. The ancient city of Wan (Nanyang) from the Han period forward was a major center of the iron and steel industry. Along with their original methods of forging steel, the Chinese had also adopted the production methods of creating Wootz steel, an idea imported from India to China by the 5th century AD.
  During the Han Dynasty, the Chinese were also the first to apply hydraulic power (i.e. a waterwheel) in working the bellows of the blast furnace. This was recorded in the year 31 AD, as an innovation by the Chinese mechanical engineer and politician Du Shi, Prefect of Nanyang. Although Du Shi was the first to apply water power to bellows in metallurgy, the first drawn and printed illustration of its operation with water power appeared in 1313 AD, in the Yuan Dynasty era text called the Nong Shu.
  In the 11th century, there is evidence of the production of steel in Song China using two techniques: a "berganesque" method that produced inferior, heterogeneous steel and a precursor to the modern Bessemer process that utilized partial decarbonization via repeated forging under a cold blast. By the 11th century, there was a large amount of deforestation in China due to the iron industry's demands for charcoal. By this time however, the Chinese had learned to use bituminous coke to replace charcoal, and with this switch in resources many acres of prime timberland in China were spared.