Development history of steelmaking process of oxygen top-blown converter

As early as 1856, German Bessemer invented the bottom blowing acid converter steelmaking method, which was the beginning of modern steelmaking method. It produced a lot of cheap steel for human beings and promoted the industrial revolution in Europe. However, this method can not remove sulfur and phosphorus, which limits its development. Thomas bottom blowing alkaline converter steelmaking method appeared in 1879, which used alkaline lining converter to treat high phosphorus pig iron. Although the converter process can produce steel in large quantities, it has strict requirements on pig iron composition, and generally cannot use more scrap steel. With the further development of industry, there are more and more scrap steel. Less than ten years after the invention of acid converter steelmaking, French Martin established open hearth steelmaking in 1864, and alkaline open hearth steelmaking appeared in 1888. Open hearth steelmaking has less strict requirements for raw materials, large capacity and many varieties, so it has become the main steelmaking method in the world in less than 20 years. Until 1950s, about 85% of the world's steel production was produced by open hearth steelmaking. 1952 pure oxygen top-blown converter appeared in Austria, which solved the problem of harmful impurities such as nitrogen in steel, made the quality close to that of open-hearth steel, and at the same time reduced the heat lost with waste gas (when blowing with ordinary air, the air contained 79% useless nitrogen), and the open-hearth pig iron could be blown at a lower temperature, thus saving the coke consumption of blast furnace and making more use of scrap steel. Because converter steelmaking is fast (it takes about 10min to smelt a heat of steel, but it takes 7 hours in open hearth), it can be used to make steel with negative energy and save energy, so converter steelmaking has become the mainstream of contemporary steelmaking.

In fact, 130 years ago, when Bessemer invented the bottom blowing air steelmaking method, he put forward the idea of steelmaking with oxygen, but it was not realized because of the constraints at that time. It was not until the early 1950s that Voest Alpine, Austria, used oxygen to make steel in industrial production, from which oxygen top-blown converter, also known as LD converter, was born. After the top-blown converter came out, it developed rapidly. By the time 1968 oxygen bottom blowing method appeared, the steel production capacity of top blowing method in the world had reached 260 million tons, occupying an absolute monopoly position. After 1970, the bottom blowing method appeared because of the invention of the double jacket bottom blowing oxygen gun with hydrocarbon protection. Various types of bottom-blown converters (such as OBM, Q-BOP, LSW, etc. ) It shows many advantages over top-blown converter in actual production, which challenges and impacts the top-blown method, which has always been in the first place.

The characteristics of top blowing method determine that it has some shortcomings, such as high iron content in slag, high oxygen content in molten steel, large loss of iron dust in waste gas and difficulty in smelting ultra-low carbon steel, and bottom blowing method can overcome these shortcomings to a great extent. However, because the bottom blowing method uses hydrocarbon cooling nozzle, the hydrogen content of molten steel is high, so it is necessary to inject inert gas for cleaning after stopping blowing. Based on the obvious metallurgical differences between the above two methods, many foreign countries began to study the top-bottom combined blowing smelting method combining the advantages of the two methods after the 1970s. Following the research on converter top-bottom combined blowing steelmaking by Dr. Eduard of Austria in 1973, the research on converter combined blowing has been widely carried out around the world, and various types of combined blowing converters have appeared, which have been officially used in production since the early 1980 s. Because it is superior to top blowing and bottom blowing, and it is easy to transform converter combined blowing on site, it has been widely used in the world a few years later, and some countries (such as Japan) have basically eliminated the simple top blowing converter.

In the traditional converter steelmaking process, the molten iron from the blast furnace is evenly mixed in the mixer, then charged into the converter according to a certain proportion, and then the water-cooled oxygen lance is lowered to blow oxygen for smelting under a certain oxygen supply, lance position and slagging system. At the end of blowing, lift the gun and pour the furnace, measure the temperature and sample the composition, such as tapping when the temperature and composition of molten steel reach the target value range. Otherwise, lower the oxygen lance and blow again. When tapping, deoxidizer and ferroalloy are added into the ladle for deoxidization and alloying. Then, the molten steel is sent to a casting workshop or a continuous casting workshop for ingot casting.

With the continuous improvement of users' requirements for steel properties and quality, the application scope of steel is wider and wider. At the same time, iron and steel production enterprises pay more and more attention to improving product output and quality, expanding varieties, saving energy and reducing consumption. In this case, the converter production process has undergone great changes. The development of hot metal pretreatment, combined blowing converter, external refining and continuous casting technology has broken the traditional converter steelmaking mode. From simple converter smelting to hot metal pretreatment-combined blowing converter blowing-external refining-continuous casting. The method is characterized by large-scale, modern and continuous equipment. Oxygen converter has changed from the original dominant position to a new process, which mainly undertakes the task of decarbonization and temperature rise of molten steel.