Chemists have analyzed and determined that the main difference between pig iron, wrought iron and steel is the different carbon content. Iron with carbon content above 1.7% is pig iron or cast iron; Iron with carbon content less than 0.2% is wrought iron or wrought iron; Iron with a carbon content of 1.7%-0.2% is called steel. Although pig iron is hard, it is brittle, steel is elastic, and wrought iron is easy to accept processing, but it is softer than steel. Pig iron steelmaking is to reduce the carbon content in pig iron and remove impurities such as silicon, sulfur and phosphorus.
In Europe, until the middle of19th century, the stirring method was still used in steelmaking. After pig iron is heated to a molten or semi-molten state, it is stirred in the molten pool, that is, the carbon in pig iron is oxidized by oxygen in the air during the stirring process. This is exactly the steel frying method that appeared in Han Dynasty in China more than 600 years ago/kloc-0. Figure 24- 1 is Song (1587-? The first edition of "Heavenly Creations" compiled by the author is about illustrations of fried steel. The book says: "Where iron is cooked, it will be cooked if it is not fried. Stir-fried is cooked, raw and cooked are harmonious, and refined is steel. "
There are more than 3,400 stirring steelmaking furnaces in the UK 1860, and 6-7 are stirred every 12 hour, each with 250 kilograms, and the daily output is 1.6 tons. This accounts for about half of the world's malleable metal production.
It is difficult to control the residual carbon content in steel by stirring furnace steelmaking, which requires a lot of manpower.
1856, the British Henry Bessemer (18 13- 1898) created the converter steelmaking method. Bessemer, the son of a mechanical engineer, fled to England during the French bourgeois revolution (1789- 1794). After leaving the rural school, he became a type worker. /kloc-started to produce metal alloy and bronze powder at the age of 0/7. He took part in the Cramer War between Britain and France (1855). After several experiments, he finally built a steelmaking furnace at 1856 in St Pancras, London.
This is a fixed container (Figure 24-2), which can hold 350kg cast iron and the air pressure is 70 ~ 100kPa. According to the Secretary of the World Metallurgical Development History (edited by Hua Jueming and others, Science and Technology Literature Publishing House, 1985), the reaction in the furnace was strong, which surprised Bessemer greatly, because he did not estimate that the reaction between oxygen and carbon and other impurities in metal was so fierce. Fortunately, after 10 minutes, when all impurities have been consumed and the flame has subsided, you can get close to the container and cut off the airflow. The metal is injected into the ingot mould and determined to be low-carbon malleable cast iron. He believes that he has found a way to make pure iron.
Soon, he made a rotatable tilting converter (Figure 24-3), each furnace can hold 5 tons of pig iron, and the smelting time is 1 hour, including the time for furnace repair and ingot casting, which greatly shortened the time for stirring steelmaking and reduced the manpower consumed by stirring smelting operation. This invention is revolutionary, and ironworkers and steelworkers at home and abroad have asked for licenses for this law.
On August 1856, 1 1, Bessel presented his invention at the British Association Conference in Cheltenham, Certo. At the same time, William Kelly, a blacksmith in Kentucky, announced in 1852 that he had invented the same method, that is, blowing air into molten cast iron to reduce the carbon content, and Bessemer bought his patent.
Bessemer was warmly welcomed and received in the early days after he announced his invention, and earned 2700 pounds in a few weeks. However, it was soon discovered that the steel ingot produced by the method he invented produced iron oxide due to excessive oxidation, and the phosphorus in pig iron could not be removed. The quality of the steel produced is very poor, either loose or hard and brittle, and it will break when forged. Bessemer was criticized and laughed at. His own steel-making plant in Sheffield 1859 can only use imported phosphorus-free iron ore.
The problem of excessive iron oxide in steel was solved by an Englishman, mushet, who has rich experience in steelmaking. Iron-manganese alloy, called mirror iron, is added to molten metal, in which manganese can reduce iron oxide.
Dephosphorization of iron ore is a long-term unsolved problem in steelmaking. Bessemer, like all other builders of steelmaking furnaces, uses siliceous materials as furnace lining. Siliceous materials will not combine with oxides generated by phosphorus oxidation, nor can they remove such stable oxides from steel. This fact makes Bessemer only use phosphorus-free iron ore, that is, iron ore with phosphorus content below 0.05%, and then make steel.
The dephosphorization problem was solved by a British court clerk, Sydney Gelchrist Thomas (1850- 1885), and 1878 succeeded. Although Thomas is a court clerk, he loves chemistry. In his spare time, he entered Birkbeck College of University of London to study chemistry, and passed the metallurgical and chemical examinations of Royal Institute of Mining and Technology. After learning about phosphorus removal in Bessemer steelmaking, he experimented with various substances, including magnesium oxide and lime, and with the help of his cousin Gelchrist (he is a chemist in this steelmaking plant), he experimented with a converter in a steelmaking plant in Bleiner. The two of them carried out experiments from 1877- 1878 for 9 months, which proved that using calcined dolomite bonded with lime as furnace lining can remove phosphorus satisfactorily, and also produced a valuable phosphate-containing material called Thomas phosphate fertilizer. Thomas won the medal of Bessemer in 1883 and became a rich man. Unfortunately, he died of tuberculosis at the age of 35. Bessemer also became a rich man when 1873 retired and was named Sir Henry Bessemer.
With the development of industry, a large number of scrap steel and scrap iron have appeared in production, construction and daily life. These scrap steel and scrap iron can not be used in converter, so open hearth steelmaking and converter steelmaking appear at the same time.
In converter steelmaking, the heat required for metal to remain liquid is provided by the heat generated by chemical reaction. However, in open hearth steelmaking, the heat generated by chemical reaction is not enough to keep the metal in a molten state, and it must be supplied by an external heat source.
1856, German engineer Charles William Siemens (1823- 1883) created an AC heat exchanger. This is to build heat storage checker brick rooms on both sides of the combustion furnace, and the hot combustion exhaust gas of the combustion furnace transfers heat to the checker brick through the checker brick room. The hot exhaust gas flow is regularly introduced into the second heat storage lattice brick chamber, and then the supplied air passes through the heated brick chamber and enters the combustion chamber with heat for combustion, thus improving the furnace temperature. Every once in a while, the flow direction of air and exhaust gas will be exchanged, so that the two regenerators alternately absorb heat from the exhaust gas. This kind of furnace was originally used to burn glass, and later it was used to make steel. It is an open hearth furnace.
William? Siemens, an engineer, went to England after receiving formal technical education in Germany. Frederick? Frederick Siemens ran an electrical company in Germany and later came to England. The two brothers think it is convenient for Britain to encourage engineers and inventors to apply for patents in Britain. 1866, they set up a Siemens factory in Birmingham, England, and used their open hearth furnace to make steel.
About the same time, French metallurgist? Pierre emile martin (1824- 19 15) also established an open hearth furnace based on the principle of heat storage, and set up a factory in Silly, France, using cast iron and scrap iron as raw materials to make steel. 1867 products were exhibited in Paris Expo and won the gold medal. Martin was awarded the Bessemer Gold Medal by the British Iron and Steel Association in 19 15.
Siemens? Martin open hearth furnace (Figure 24-4) includes four heat exchange chambers, which are filled with refractory bricks arranged in a grid. Air enters combustion chamber IV through pipes A and B, and combustion gas enters combustion chamber III through pipes D and E. The combustion gas is a mixture of producer gas, coking gas and blast furnace gas. The two gases are mixed and burned at ⅴ, and the generated gas passes through I and II chambers to preheat the checker bricks in the two chambers, and the cooled gas passes through C and enters the chimney. Rotate pistons F and G to make air and combustion gas enter into chamber I and chamber II, mix and burn in chamber VI, and preheat chamber III and chamber IV. ⅶ is a heat exchanger, and the temperature can reach 1800℃. A proper proportion of scrap iron and iron ore are mixed together and melted at ⅶ℃. Some impurities in iron are oxidized by air and some by iron oxide. The whole process takes about a few hours.