Heat treatment in ancient China
Heat treatment of materials has a long history in China. Compared with other parts of the world, the development of ancient Chinese heat treatment technology has obvious regional characteristics. In some respects, China's heat treatment technology lags behind other regions, but there are also many inventions and technologies in the world's heat treatment history, which is not far ahead. Less results have spread to all parts of the world and have directly contributed to the advancement of world heat treatment technology.
The development of material heat treatment technology in China is similar to other technologies. Traditional heat treatment technology has experienced the process of introduction, digestion and development of modern technology from germination, establishment, development, prosperity to weakness. Referring to the ancient stage of China, it can be said that in ancient times, China's heat treatment has begun to sprout. In the ancient times, China's traditional heat treatment technology began to be established; in the Middle Ages, China's traditional heat treatment technology was further developed; in the ancient times, China Traditional heat treatment technology has reached its peak. In the modern era, China's traditional heat treatment technology has gradually weakened, and modern technology has begun to be established and developed.
In ancient times, China's heat treatment has already sprouted. The basis for the development of ancient heat treatment technology is fire. The use of fire cannot be ignored. In the Paleolithic era, fire was mainly used for heating lighting to cook and drive the beasts. Chinese ancient humans have a tradition of using fire. At the latest in the sacred period of Beijing 460,000 years ago, our ancestors had learned to use fire. The existing archaeological data indicates that the ashes found in the caves where the cavemen of Zhoukoudian Beijing lived are one of the earliest relics of the world's recognized human fire. The ancient Chinese ancestors used fire for material heat treatment from the Neolithic Age. In the early Neolithic period, the ancient ancestors often dealt with the soil in labor and life. After discovering that the soil was mixed with the right amount of water, it would be sticky and malleable, and could be randomly shaped into various shapes by hand. The mud is cool and hard, and it can hold things, but the mud is afraid of water. Over-fired mud is not afraid of water, which may be due to an accidental discovery. From then on, due to the fire, the clay was transformed into a long-lasting, fire-resistant, water-resistant pottery due to heat treatment. This is the earliest example of human consciously performing heat treatment. According to the existing archaeological data, China's pottery appeared in the world's earliest pottery from 7,000 to 10,000 years ago. Most of the early pottery was subjected to heat treatment at a temperature of about 750 to 1000 ° C, which caused high-temperature transformation of clay minerals such as quartz, mica and feldspar in the mud. Since then, people have been practicing the selection and firing conditions of pottery, which has made China's early ceramic technology far ahead of the rest of the world. Ordinary clay pottery is easy to break. Our ancestors have invented a certain amount of sand in the soil. Because of the sand-burning in the clay, the expansion coefficient of the material is reduced, and the resistance to cold and heat is greatly improved. . Sand-filled pottery is found in many Neolithic sites.
During the Xia Dynasty and the Shang Dynasty, ancient Chinese ancestors began to understand metal, metal processing and metallurgy. The history of human application of copper dates back to 7250 BC. The invention of the annealing process should be said to be the beginning of heat treatment of human metals. Studies have shown that early copper and its alloys are not suitable for large-scale processing without annealing. Copper and its alloys are prone to work hardening, and intermediate annealing produces recrystallization to soften the copper alloy for further processing. This technology is widely used in the manufacture of weapons and household appliances. The processing of bronze by foreign processes using forging and annealing has long appeared. The history of the application of copper and its alloys by ancient Chinese ancestors was later than that of the two rivers. According to the excavated early objects, some believe that metallurgy has sprouted in China about 5,000 BC. The earliest metal relics known in China so far are copper sheets and tubes excavated in the first phase of the Yangshao culture Banpo type in Linyi Jiangzhai. In addition, there are about 6,000 years of red copper shards unearthed from the Dawenkou Cultural Relics in Shandong Province and the red copper ring of Liaoning Jianping from the Hongshan Cultural Site of Niuheliang. It can be argued that ancient metal relics that appeared around the 7th to the 3rd centuries BC have shown that metal technology has begun to sprout on this land. Especially during the Longshan culture period in the second half of 3,000 BC, there were more than 50 pieces of 11 types of unearthed bronzes in China. The bronzes of the Longshan culture period belong to small tools and ornaments such as knives, cones, chisels and drills. The forming methods are cast or forged, and some cutting tools may be annealed during processing. The analysis of the bronze cone of the 1700 BC unearthed from the Qinweijia site in Yongjing, Gansu, by the Metallurgical History Group of the Beijing Iron and Steel Institute, showed that the matrix structure is recrystallized solid solution, coarse grains, and α+δ eutectoids along the processing. The direction is deformed and it is apparent that the tissue has undergone recrystallization annealing. Ancient weapons such as swords, scorpions, axes, and gems need to be forged into a sharp edge. In order to prevent cracking during the forging process, forging annealing is required. "Forging Nai Ge Ge" is a record of the production of weapons in the Shang and Zhou dynasties. Effective application of annealing technology can produce a sword with complex and sharp shapes.
Annealing is also applied in vermiculite processing. The bismuth iron is actually a high-iron nickel alloy. Humans living in the two river basins began using this "God-given" metal more than 3,000 years before BC. In order to make tools or small items, they use an annealing or forging process. This is the earliest heat treatment of steel in mankind. In China, seven pieces of bismuth iron products were found in the Shang and Zhou ruins, and there were traces of forging and annealing. The oldest of them was the Iron Blade Causeway, which was unearthed in the 14th century BC, unearthed from the Shang Dynasty site in Taixi Village, Yucheng, Hebei Province in 1972. There are high and low nickel layered structures in the iron blade, and it is confirmed that it is forged from strontium iron with a high nickel content. Another item was found in 1977 in the Shang Dynasty tombs in Liujiahe Village, Pinggu County, Beijing. The iron blade is forged to a thickness of about 2 mm. This iron blade copper beak has obviously undergone forging and annealing. In contrast, China's ferroniobium processing is later than the two river basins. Whether the annealing of these products is done by Chinese ancestors is still controversial in the international archaeology community. A considerable number of scholars abroad believe that this item is likely to be introduced from the Middle East or other parts of Asia. They believe that China has a short history of iron and was not able to carry out similar metal processing at that time.
Annealing was used in the processing of natural gold in the Shang Dynasty. Natural gold is mainly derived from the frit of natural gold nuggets and gold dust. An important use of gold in the early days was to make thin gold or gold pieces to decorate the objects. In the early days of foreign countries, cold working was usually used to reduce the thickness of gold pieces to a few hundredths of a millimeter. Most of the gold products unearthed in China are ornaments, such as golden armbands, gold earrings, gold dragonflies, gold leaves, etc., and there are quite thin gold foils in the unearthed Shang Dynasty remains. For example, the gold foil unearthed from the Tomb of Yinshang in Anyang, the thickness of the gold foil is 0.01±0.001mm. It is analyzed by the teaching and research section of the Metallurgical History of Beijing Iron and Steel Institute. The grain size is uniform and the grain boundary is flat. It is considered to be made by forging and annealing. of. Due to the large-scale decoration needs of China in the early stage of construction, etc., Chinese artisans were encouraged to apply annealing treatment in the processing of gold foil. The application of annealing makes the Chinese Shang Dynasty have gold foil.
The Zhou Dynasty, especially during the Spring and Autumn Period and the Warring States Period, was the beginning of China's iron smelting. Solid carburizing steel was produced during this period. Solid carburizing is a process technology that uses a workpiece to be buried in a solid carburizing material. It is one of the oldest heat treatment technologies. China's solid carburizing treatment began around the Spring and Autumn Period, and its age was around 7 BC to 6 BC, which was the beginning of metal chemical heat treatment. Solid carburized steel can make sharper and slender weapons, and is a replacement weapon material. The ancient Chinese literature "Yueshushu" has described this. "When the Yellow Emperor was in the jade, he used the jade as the soldier. When he was acupoints, he used copper as a soldier. When this was the case (in the text, the Spring and Autumn Period, the author's note), iron Soldiers, defending the three armies." The application of solid carburizing steel in China is behind the birthplace of foreign iron industry for about ten centuries. Products made by solid carburizing are called fast iron. There are not many iron-making blocks unearthed in China. Archaeological evidence has confirmed that medium-carbon block iron-iron carburizing steel has appeared in the late spring and autumn tombs. For example, the analysis of the steel swords in the late Spring and Autumn Period unearthed from Yangjiashan, Changsha, Hunan shows that its carbon content is about 0.5%, which is a piece of iron-iron carburized steel products, which was around the 6th century BC.
During the Warring States period, a remarkable achievement of ancient Chinese heat treatment was the invention of cast iron softening. After a large number of archaeological studies, the invention of China's cast iron was about mid-spring. The earliest cast iron fragments have been unearthed in the Tianma-Qucun Jin culture tombs in Shanxi. Ten products were also discovered in the early days of the Warring States with white cast iron. In order to overcome the brittleness of white cast iron, Chinese artisans invented the annealing technology suitable for the softening treatment of cast iron in the fifth century BC. The iron shovel unearthed in the early ash pit in Luoyang, Henan Province, has an internal structure of Leysite and has a surface. A pearlite belt of about 1 mm. The presence of the pearlite layer makes the white cast iron tough, and it is obvious that this is the structure obtained by annealing. There is also an iron unearthed in the same pit as the iron shovel. The iron has been basically embroidered, and its residue has been metallographically tested. The matrix structure is a ferrite decarburization layer, and the graphite structure is a relatively complete flocculent annealed graphite. It can be considered that this is an expanded cast iron obtained by annealing. It is analyzed that it is subjected to long-time annealing at 900 ° C or slightly higher temperature to decompose cementite to obtain agglomerated graphite. The appearance of the same type of malleable cast iron in Europe is after 1720.
According to the archaeological analysis of cultural relics, ancient Chinese quenching technology may be first used in block iron making. A quenching object of archaeological excavation is a steel sword unearthed from the late Warring States Period of the Yanwu Duwu Balcony Village in Yi County, Hebei Province. The carbon content is 0.5% to 0.6%, and the whole blade body is composed of a high carbon layer and a low carbon layer, and the blade portion is mainly composed of quenched martensite. This is a quenched structure of a typical block-smelting carburized steel stack forging. After forging the block to iron, the iron absorbs the carbon and reduces the inclusions into steel. This steel has a tight structure and uniform carbon content and is suitable for the production of weapons and tools. The further development of this steelmaking technology is the "100 steelmaking" technology. The metallographic analysis of steel products during the Warring States period also found that there are similar tempering and normalizing organizations inside the steel. Chinese artisans may unintentionally apply a process similar to tempering and normalizing, thus expanding the use of steel products.
The surface treatment of metal in ancient China mainly consists of “golden goldâ€, “silver silver†and tin plating. The most commonly used is the amalgam method, in which the metal to be plated is dissolved in mercury and then coated onto the substrate by wiping. This technique is generally applied to the decorative treatment of bronzes. It is known that the early sheet metal objects were the long-armed gongs unearthed from Qufu, Shandong Province. The tombs were the turn of the Spring and Autumn Period and the Warring States Period. Tao Hongjing later pointed out the role of amalgam: "Mercury can digest gold and silver, make it into mud, and people use plating." Ancient Chinese glass manufacturing began to develop in the Zhou Dynasty. In 1976, in the Xizhou urban site excavated in the Rujiazhuang area of ​​Baoji, Shaanxi Province, four different forms of glass flat plants and green glass tubular necklaces were found. In addition, in the tombs of the Warring States in Jincun, Changsha, Huixian and other places, a number of white, emerald green, dark green glass products were unearthed, the color is beautiful, and most of them are translucent. According to analysis, most of them are lead-bismuth glass with high lead content and high amount of lead. There is a big difference in composition between the “soda-lime glass†that is common in the West. "Leading glass" has a low processing temperature, and although it has the characteristics of colorful and crystal, it has the disadvantages of fragility and poor transparency.
The Qin and Han Dynasties were a period of vigorous development of iron and steel scales in China. The shaft furnace of the Western Han Dynasty has developed to a considerable scale. The restoration of the cast iron furnace refractory bricks unearthed in Nanyang shows that the shaft furnace at that time was about 3-4 meters high and 2 meters in diameter. The Eastern Han Dynasty's Taishou Du Shi also invented a much more efficient water platoon. Moreover, in the Han Dynasty, the technology of frying steel has been popularized, and ferritic iron can be produced by this technology. The corresponding ancient heat treatment process also showed a comprehensive development. Craftsmen of this period have made great progress in mastering and applying steel annealing. In addition to the intermediate annealing of the forgings, the use of annealing as the final heat treatment seems to have been adopted by ancient artisans. The contemporaries of the Han Dynasty tombs of Mancheng No. 1 and the twenty sons of Hohhot are all pieces of iron-making materials. From the microstructure of the surface layer, they are ferrite structures, and the final treatment process should belong to the annealing process. . In addition, the former Beijing Iron and Steel Institute Metallurgical History Research Office conducted a metallographic survey of 188 pieces of Han Dynasty ironware unearthed in Henan. The results show that 40% of the irons in the census are steels obtained by decarburization of cast iron. Most of the tools are made of pearlite and cementite, and even some of the cementite has been spheroidized. It can be seen from this that ancient artisans performed long-term annealing on medium and high carbon steels around 723 ° C. They used this method to obtain spheroidized annealed structures in some cases. The decarburization treatment is a chemical heat treatment. This technology has been widely used in the Qin and Han Dynasties to process white iron. The graphite inside the gray iron is in the form of flakes, which is a cast iron with good performance. The contemporary gray iron is realized by adding a graphitizing element and controlling the cooling rate. In ancient China, the gray mouth organization was acquired very early. The teaching and research section of the Metallurgical History of Beijing Iron and Steel Institute once examined the ironware of the Han Dynasty and found that gray iron accounts for 21% of the cast iron and 4% of the tinplate. They believe that the production of gray iron in the Han Dynasty is a mature technology, and the tinplate is It was accidentally obtained when producing gray iron. Ancient craftsmen seem to have known the performance characteristics of gray iron. The axles of 112 years before the cemetery unearthed in Mancheng Han Tomb are made of gray iron. The structure has graphite, which can play the role of wear resistance and friction reduction. This is the earliest gray iron that was discovered. Since the gray content of the ancient gray iron is lower than that of the modern gray iron, the acquisition of the gray mouth structure is likely to be the product of the graying annealing treatment. Of course, the gray iron in the Han Dynasty may also be obtained by controlling the cooling rate of solidification. But it is more likely that the cast iron is subjected to a high temperature annealing method in the kiln. More notable is the appearance of spheroidal tissue inside the irons that were censused. Spherical graphite was found in the identification of the iron vessels of the Dianchi Hanwei. The analysis of some irons with spheroidal graphite by archaeologists in our country shows that the morphology, structure and mechanical properties of spheroidal graphite are no different from those obtained by adding spheroidizing agents. The spheroidization grade reaches the level 1-2 of the modern nodular cast iron metallographic standard. The foreign researchers determined the spheroidizing annealing process of cast iron after observing the metallographic phase of the unexpectedly obtained high-toughness cast iron in 1942. The Han Dynasty also made great achievements in quenching. The "100 steelmaking" invented during this period was mainly used to manufacture weapons. The number of steels folded and forged is many, the carbon content is more, the structure is more fine, and the composition is more uniform, so the quality of steel is greatly improved. In the middle and late Western Han Dynasty, China has also developed a new steelmaking technology "fried steel", which is a new steelmaking technology developed on the basis of pig iron smelting technology. Fried steel technology is a breakthrough in steelmaking technology. It can provide a large number of cheap, high-quality wrought iron or steel to meet the needs of production and war. The emergence of fried steel has also greatly promoted the development of the technology of the hundred steelmaking. People can use the fried steel as raw material, and repeatedly heat, fold and forge into a steel piece of good quality. The steel swords of the first two years of the Emperor Yongdi in the six years of Emperor Yongzheng, unearthed in Cangshan, Linyi, Shandong, and the second year of the Emperor Jiandi, unearthed in Xuzhou, were recorded with the words "Thirty" and "Fifty". During this period, ancient craftsmen also invented partial quenching, and the metallographic analysis of the four chisels unearthed from the Tomb of the King of the Lions in Xuzhou, Xuzhou, showed that the four chisels were partially quenched by the cutter head to obtain the cutter head. Hard, knife body tough effect. The analysis of the ring steel knife unearthed at the Han Tomb in Cangshan, Shandong, the steel sword of Fufeng Han Tomb in Shaanxi, and the Liu Sheng wrong gold book knife in the Han Dynasty also showed that these swords only observed martensite in the blade, and the ridge of the sword was not quenched. organization.
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