The hard and tough iron that Bessemer wants to smelt is actually steel. But at that time, he knew nothing about smelting iron, so he learned it from scratch. First of all, learn from the basic knowledge of iron smelting. In a short period of two or three years, Bessemer has read almost all the books on metallurgical problems. At the same time, he also visited the iron-making factories all over Britain, and inspected the iron-making methods at that time in detail. In order to combine the theoretical knowledge in books with the practice of steel production, he also set up a factory to carry out experiments. After studying hard, he finally mastered the basic knowledge of smelting iron. In the era of Bessemer experiment, there were basically only two kinds of iron used in manufacturing. One is cast iron, which is pig iron. It has high carbon content and is hard, but it is also brittle and has low tensile strength. It is mainly used for casting engine cylinders, frames and other products after smelting. Pig iron is hard and brittle and easily broken, which is one of its main defects. The new cannon designed by Bessemer is made of pig iron. The other is forged iron, which has much greater tensile strength and elasticity. Because wrought iron is soft, rails, hulls, bridges and various machine parts can be made by forging, pressing and other molding methods. This kind of iron is easy to deform under high pressure because of its soft texture, so its use is also greatly limited. The iron directly produced by the ironmaking furnace is pig iron, and the carbon content of pig iron is very high, above 2%. Try to remove the carbon contained in pig iron to get wrought iron. The carbon content of wrought iron is generally below 0.04%. The carbon content between them is steel. Compared with pig iron and wrought iron, steel has excellent properties, both hardness and toughness. But at that time, steel was difficult to manufacture, so it was very expensive and was regarded as a precious metal. It is obviously unrealistic to use it to cast guns. Of course, if we can find a cheap and fast steelmaking method, it is another matter. Now, what Bessemer has done is to find this way. The traditional steelmaking method is to first convert pig iron into wrought iron, and then add a proper amount of carbon to make steel. In order to change pig iron into wrought iron, oxidation method was adopted at that time, that is, oxidant (usually iron ore) was added to pig iron and heated to make it in a molten state. At this time, the carbon in the molten pig iron will react with the oxidant and be removed. Bessemer carefully studied the method of changing pig iron into wrought iron. He added carefully weighed iron ore to pig iron, and then heated the mixture to make it melt. The main component of iron ore is iron oxide. At high temperature, oxygen atoms in iron oxide combine with carbon atoms in pig iron to generate carbon monoxide, which is further burned to escape as carbon dioxide. At this time, all that is left in the furnace is wrought iron. According to the experimental results, Bessemer thought: Since carbon atoms in pig iron can be oxidized to obtain wrought iron, why can't carbon be burned by other oxidation methods? For example, a blower directly blows air into molten pig iron, so that oxygen in the air reacts with carbon atoms in molten pig iron to decarbonize it, thus obtaining wrought iron. Bessemer's suggestion met with opposition from some experts. These experts believe that when molten pig iron is blown by a blower, the cold air blown in will cool and solidify the molten iron, which will lead to the stop of the whole smelting process.

Bessemer didn't blindly listen to experts' opinions. Whether he thinks his suggestion is feasible depends on experiments. The experimental result is contrary to the expert's opinion. The blowing wind not only did not cool the molten iron, but increased the temperature of the molten iron, because the oxygen atoms in it reacted with the carbon in pig iron to release heat. In the first experiment, when the blower blew the molten pig iron, it suddenly burned in the already calm iron smelting furnace, and the reaction was extremely intense and almost out of control. This made him very nervous. He didn't expect that carbon and other impurities in molten iron would release so much heat when they were oxidized. Fortunately, this process only lasted for ten minutes. After the oxidation, he was relieved. Experiments show that the blast method does not need additional fuel, reduces the cost and is simple and easy to operate. This is indeed a good method of pig iron maintenance. With the deepening of the experiment, Bessel further thought that in the process of pig iron curing, if the reaction is stopped at an appropriate time, the carbon in pig iron is not completely removed, but kept within the range of 2% ~ 0.04%, and steel can be directly obtained. There is no need to extract wrought iron from pig iron first, and then obtain steel through wrought iron stage, as in the traditional method. Of course, there is no need to spend a lot of money on fuel in these intermediate processes. In order to verify the feasibility of this idea, he built a fixed melting furnace in his factory in St. Pancris, London. The furnace is about1.2m high and can hold 350kg pig iron. There are six tuyeres at the bottom of the stove. Bessel did a serious experiment with it, and the experimental results proved that his idea was completely feasible. So,1August, 856, he gave a report entitled "Method of making wrought iron and steel without fuel" at the annual meeting of the South British Association for the Advancement of Science in Cheltenham, introduced his steelmaking method, and sent the carefully written paper to the magazine for publication. Since then, his blast steelmaking method has been officially announced to the world. 1860, the first improved mobile converter was built and put into operation. People generally call this kind of furnace "Bessemer converter". Because acidic materials are used as furnace lining, this steelmaking method is also called "acid bottom-blown converter steelmaking method".