Chapter 8 Section 5 Various Iron and Steel Smelting Processes in Ancient China

my country's artificial iron smelting was later than West Asia's Mesopotamia and Egypt.According to the existing records and the investigation of unearthed cultural relics, it can be roughly traced back to the Spring and Autumn Period, and the earlier legends and speculations are not very reliable. "Zuo Zhuan" records that in the Spring and Autumn Period, Zhao Yang, a native of Jin State, led his army to Rubin, where he expropriated pig iron and cast a punishment tripod, on which Fan Xuanzi's punishment book was cast. The book "Guanzi" (although it was written by later generations entrusted by the name of Guan Zhong, the book was written later, but the content is mostly based on the archives of the Qi State government in the Spring and Autumn Period) once recorded: "There are five thousand three hundred and seventy-one famous mountains in the world,... There are nine out of three thousand and six hundred iron mountains.""Wuyue Spring and Autumn" written by Zhao Ye, a man of the Eastern Han Dynasty, said: In the Spring and Autumn Period, King Helu of Wu ordered craftsmen to "collect the iron essence of five mountains" to forge swords. With the assistance of his wife Mo Xie, he finally forged two extremely sharp swords. famous sword.These records are of great reference value.From the unearthed cultural relics, the earliest iron smelted by man can be listed as follows: a bronze sword with an iron handle in the late Spring and Autumn period was unearthed in Lingtai, Gansu; an iron bar and pig iron pellets in the late Spring and Autumn period were unearthed in Chengqiao, Liuhe County, Jiangsu; A pig iron shovel (shovel) was unearthed from the Chu tomb at Shiziling, Changsha; an iron tripod cast by Chu State was unearthed at Yaoling Mountain, Changsha.From the time point of view, it is roughly consistent with the literature records.Of course, in earlier times, our ancestors had contact with meteorite, but it was not artificially smelted.For example, in 1972, a bronze ax was unearthed in Taixi Village, Gaocheng County, Hebei Province in the mid-Shang Dynasty. It was inlaid with an iron blade. After scientific identification, it was inlaid and cast on the copper ax with meteorite.So how to identify artificially smelted iron and meteorite?There are two main reasons: one is that the ancient artificial iron smelting must contain more silicate inclusions, but there will be no meteoric iron.Second, meteoric iron always contains a relatively high content of nickel (about 5%) and some cobalt, and the content of nickel and cobalt in iron shows a high and low distribution.

In ancient times, the raw material for ironmaking was mainly iron-rich ore (hematite).After it is mixed with charcoal, it is placed in a smelting furnace and ignited and blasted for smelting.The burning of charcoal not only causes high temperature, but also produces carbon monoxide, which reduces iron oxide.In fact, the smelting temperature required is above 1000°C.According to the general law of development, the original iron smelting may only use natural ventilation or blow with leather sticks, and the temperature will not be too high.The iron produced will not be liquefied, so the product is iron in a semi-molten state. Other unreduced substances and rock impurities (slag) in the ore cannot be separated out, so they form a frit with iron, so it has to be forged repeatedly while it is hot. Squeeze out most of the inclusions.This kind of iron is called lump iron.It takes a lot of work to produce this kind of iron, the labor intensity is high, and the production efficiency is also low.But it contains very low carbon, close to pure iron. Although it has a high melting point, it is flexible and easy to forge.With the improvement of smelting technology, people continue to increase the height of the iron-making furnace and strengthen the blast. The iron-making furnace gradually develops from the pit type to the shaft furnace type, and the combustion intensity will increase, and the production rate will increase.But it also causes new problems. As the smelting temperature increases, the amount of carbon infiltrated in the iron will also increase, and the silicon, sulfur, and phosphorus in the ore will also infiltrate into the iron after reduction, so that another type of carbon will be obtained. Iron, that is, pig iron.Due to impurities such as silicon, sulfur, and phosphorus, the melting point will drop to about 1150°C.Although it is easy to obtain molten iron, it can be separated from the slag well, and it is also convenient for casting, and the pig iron is hard and wear-resistant.But there are also serious disadvantages, that is, it is very brittle and almost completely loses the performance of forging.

From the perspective of the history of iron smelting progress, it is worth noting that pig iron and block iron smelting appeared at the same time in my country, while in Europe, although block iron smelting technology was mastered very early, pig iron was not used until the 14th century.The reason why my country was able to smelt pig iron in an earlier period is probably related to the high development of my country's bronze smelting technology.Because if the blast furnace found in the Tonglushan copper smelting site is strengthened, it is possible to smelt pig iron with the addition of iron ore.

These two iron-smelting processes have coexisted for quite a long time in our country.Although the work efficiency of block ironmaking is low, the process and equipment are simple, and the product has excellent forging performance. It can be made into steel by carburizing in charcoal fire. Therefore, it is an important raw material for forging iron and steel in ancient times. It adapted to the social forging at that time. The need for weapons and tools.Since the late Spring and Autumn period, almost all the utensils forged with lump iron or carburized steel as raw materials have been found.For example, forged iron tools were unearthed from the Tonglushan ancient mine in Daye; iron chisels were unearthed from the tombs of the middle and late Warring States Period in Banpo, Xi'an; various types of forged weapons were unearthed in Yanxia, ​​Yi County, Hebei; The armor of Liu Sheng, King Jing of Zhongshan (made up of 2859 pieces of wrought iron), they are all made of iron.Even after the technology of frying steel was developed at the end of the Western Han Dynasty, block iron smelting was still popular, such as the ironware unearthed from the brick and stone tomb of the Eastern Han Dynasty in Shunyi County, Beijing, the iron scissors unearthed from the tomb of Prince Yide in the Tang Dynasty in Shaanxi, and the outside of Shuncheng Gate (now Xuanwu) in Yuandadu, Beijing. The long iron knives unearthed in the gate) were all forged with a piece of iron (or fried steel).

In ancient my country, four varieties of pig iron were successively developed.White cast iron appeared the earliest. The aforementioned iron pellets unearthed from Chengqiao, Liuhe County, and the iron tripod unearthed from Changsha are both typical white cast iron products.The carbon contained in it exists in the state of iron carbide. This kind of pig iron is hard and brittle, and the fracture is silvery white.Its advantage is that it is wear-resistant, so it is suitable for making agricultural tools such as plowshares.Our ancestors quickly found a suitable use for it.The second type of pig iron is gray iron, because it contains more silicon, which can promote the graphitization of carbon in iron.Therefore, the small pieces of graphite make the cross section of this iron gray, and the matrix becomes iron with low carbon content, so its brittleness is reduced.This kind of iron has good casting performance and small solidification shrinkage, so it is suitable for casting more delicate items.At present, the earliest gray iron comes from the Han Tomb in Mancheng, and it is used to make the mace (bearing) on ​​the car.Because gray iron contains graphite flakes, which have a certain lubricating effect, making bearings is its specialty.The third type is mottled iron, whose performance is between the above two kinds of pig iron, and mottled iron products have been unearthed in Tonglushan and Mancheng Han Tombs.The fourth is ductile cast iron.When white iron is heated, kept warm, and cooled slowly, the carbon in it will be precipitated as flocculent graphite, and the matrix is ​​equivalent to low-carbon steel or medium-carbon steel. This process is now called "annealing". In ancient my country, this This process is called "softening treatment", and the pig iron obtained is ductile cast iron, which is a major invention in the history of metallurgy.Our ancestors began to explore this kind of processing technology as early as the Warring States Period, and it was widely developed during the Han Dynasty to the Southern and Northern Dynasties.There are too many ductile cast iron artifacts unearthed.

Historically, pig iron was mainly consumed in casting various farm implements and vehicles.In addition, there are some other uses, which are interesting to say.After the Southern Song Dynasty, a large amount of pig iron was used to cast cannon bodies. Some cannon bodies were several meters long and weighed from hundreds to thousands of catties; The stones of Zhouqiao were originally filled with pig iron water, so it is no wonder that they are extremely strong. This process is called "metallurgical solid gap"; The first big iron man is a large pig iron casting in the Zhao and Song Dynasties; the big iron pot of Nengren Temple in Yandang Mountain, Zhejiang Province, has a diameter of 2.2 meters.In addition, there are many iron towers cast in ancient times. There is an iron tower cast in the Jiajing period of the Ming Dynasty in Mount Tai, with 13 floors and a total height of more than 10 meters.

If our ancestors summed up a wealth of experience in the production and utilization of pig iron, then they contributed more ingenuity and wisdom and exerted greater creativity in exploring various steelmaking processes.It can be said that my country is one of the first countries in the world to produce steel. If we put aside those unreliable legends and conjectures, more conclusive records and unearthed cultural relics can prove that as early as the late Spring and Autumn Period, shortly after the birth of iron smelting, the transition to steelmaking. A copper grid iron sword was unearthed from Chu Tomb No. 65 in Yangjiashan, Changsha (late Spring and Autumn Period). Metallographic examination proved that it was made of steel. This is the earliest steel utensil discovered so far.Steel swords were also unearthed in Yanxiadu during the Warring States Period in Yi County. After testing, the mystery of steelmaking technology during the Warring States Period was revealed.It is made of a block of iron, and it is forged on a charcoal fire. While the inclusions are being expelled, the charcoal seeps in from the surface, so there is a phenomenon that there is more charcoal on the surface and less charcoal inside.After forging, the iron sheet is extended, and the craftsman folds it up and continues to forge, and forges several pieces to form the sword body.Therefore, on the cross-section of the sword, a layered structure containing high and low carbon is formed.This is the oldest steelmaking method of so-called carburized steel in China.The process is relatively simple, and the required temperature is relatively low. Of course, the production efficiency is also relatively poor, and the quality is not very good.It is also worth mentioning that some of the carburized steel unearthed in Yanxiadu have been quenched.Perhaps at the beginning, in order to cool the forged sword faster, the craftsmen dipped it in cold water while it was hot, and later found that doing so could make the steel hard, so a special quenching process was gradually formed.

In the process of refining carburized steel, craftsmen will of course find that the more times of repeated heating and forging, the tougher the steel will be, so they developed the steelmaking process. "Hundred refining" can make the composition of steel homogeneous, reduce and refine inclusions, and significantly improve the quality of steel.This kind of steel can be regarded as the highest quality variety among ancient steel materials in my country.Metallurgical historians have examined Liu Sheng's sword in the Han tombs in Mancheng.This is exactly what is said in "Hanshu Wang Baozhuan": "Skillfully casts the simplicity of a general, and clear water quenches his edge." This shows that the quenching process has reached a mature stage in the Western Han Dynasty.Although the quality of this kind of steel is very high, it is conceivable that "thousands of tempering" is very hard work.It is said that Cao Cao once asked a famous craftsman to refine five precious swords for him, and it took three years.He called this kind of knife "Baipi knife", which means that it is so sharp that even ghosts and ghosts will be scared away by it.It is also because of the hard forging and exquisite craftsmanship of this kind of products that they are praised by later generations.According to legend, Longquan County, Zhejiang Province is the place where Ou Yezi once made swords. Later generations built Ouye Temple, which is still the origin of "Longquan Sword". Hundreds of years of traditional steelmaking technology.

In the late Western Han Dynasty, a major technological innovation occurred in the history of steelmaking in my country, and a new process of making steel with pig iron was created, that is, "fried steel".Stir-fried steel is to heat the pig iron until it is melted or basically melted, then put it in a ceramic molten pool to continue heating and stirring continuously, and use the oxygen in the air to partially oxidize the carbon, sulfur, phosphorus, etc. in the pig iron to become steel (Fig. 2-4).Of course, in terms of ancient technical conditions and knowledge levels, it was difficult to control the carbon content in fried steel in an ideal state, and often the pig iron was fried into wrought iron after frying to the end, so fried wrought iron and fried steel are essentially equal. It's the same thing, wrought iron is fried steel with very little carbon.After the Eastern Han Dynasty, with the emergence of the new technology of frying steel and wrought iron, some steelmakers switched to using wrought iron as raw material.Unearthed in Cangshan, Linyi, Shandong, is a "Thirty-refined" broadsword made in the sixth year of the Yongchu period of the Eastern Han Dynasty (AD 112).The quality of this kind of refined steel is extremely high, and most of the famous swords and swords after the Eastern Han Dynasty were forged by this process. "Book of Jin" records that there is a hundred-smelting steel knife called "Daxia Longque", which is known as "Famous China" and "Weifu Nine Districts", and it is probably forged from fried steel.

Around the period of the Jin Dynasty and the Southern and Northern Dynasties, another unique technology of "irrigating steel" came out.The scientific principle of this steelmaking process is based on the fact that pig iron contains too much carbon, making it hard and brittle, while wrought iron has too low carbon content, making it soft and not firm.Compared with wrought iron, pig iron has a relatively lower melting point. If the pig iron and wrought iron are combined and heated together, the pig iron will melt and penetrate into the wrought iron, and the properties of the two will be compromised. , smelted into steel" (Song Yingxing Yu).This kind of steelmaking technology has been clearly recorded in the Southern and Northern Dynasties. At that time, Tao Hongjing, a master of medicine and alchemy in the Southern Dynasties, said: "Steel is made of miscellaneous refining and raw 鍒 [rourou, referring to soft iron, that is, wrought iron]. The sword and sickle." A Taoist priest in the Eastern Wei Dynasty, Qi (qiqi) Wu Huaiwen, used this steel to forge a precious sword, which he called "Su Tie Dao", which was said to be extremely sharp. Folded into 30 pieces, the knife was raised and lowered, and it was cut into two halves.So why is it called "Su Tie" knife? "Book of Northern Qi·Fang Ji Biography" explains: The steel used in this kind of knife is to make pig iron and wrought iron live together, just like the mating of two sexes. So into steel.The craftsmen at that time did not have much scientific knowledge about steel and iron, but they were able to sum up this ingenious method from the long-term steelmaking experience of their ancestors, which is really amazing and admirable.In the Song Dynasty, the technology of pouring steel became more mature, and the famous book "Mengxi Bi Tan" by Shen Kuo, a scholar of the Northern Song Dynasty, introduced it more clearly.At that time, wrought iron rods were bent and wound into coils, pig iron blocks were embedded between the rods, sealed with mud, put into the furnace for smelting, and after being smelted, they were taken out and hammered into steel.He said that this kind of steel is also called "group steel".This craft was still very popular until the Ming Dynasty.Song Yingxing's "Tiangong Kaiwu" also has a detailed introduction.

In short, although my country's iron smelting technology rose relatively late, pig iron smelting and steelmaking technology came from behind, making rapid progress and continuous innovation. In the history of world iron and steel development, it was at the forefront for a long time before the Ming Dynasty.