In the annals of industrial progress, certain processes stand as unsung heroes, quietly shaping the landscapes of innovation. The Open Hearth Process, a stalwart method in metallurgy, embodies such quiet heroism. Born out of necessity in the 19th century, this pragmatic approach to steel production has left an indelible mark on the modern world. Stripping away the glamour often associated with technological breakthroughs, the Open Hearth Process thrives on simplicity and functionality, providing a reliable foundation for the steel industry’s growth.
Intro
History of open hearth process can go back to 1861. At that time, Siemens invented gas producer, used gas to replace coke as fuel. Three years later, french industrial engineer Martin consummated furnace under the guide of Siemens, he made premium steel with pig iron and steel scrap successfully. In 1868, Siemens also made steel using pig iron and iron ore by this method. In addition, he found out the fact that if add some alkali substances during steelmaking, it will solve dephosphorization’s problem, it makes this method is suitable to promote in Europe. Due to the shape of furnace is low and smooth with a flat molten pool, that was called “open hearth”, “Siemens Martin open hearth process” or “Martin furnace”. Not only pig iron, molten steel, but also steel scrap, iron ore as raw material used in this process, and smelted steel is even, quality is superior. Thus, the steelmaking system——“open hearth as dominant, converter as supplementary” developed rapidly all over the world and still in use.
Major raw material
Steel scrap, iron scrap, iron ore and limestone are mainly used in open hearth process.
Overall technique process
Overall technique process of open hearth steelmaking is divided into 5 steps generally, these are as follows:
Repairing Phase:
The period from the completion of steel tapping in the upper furnace to the introduction of the first batch of materials in the lower furnace is generally referred to as the repairing phase.
Charging Phase:
The time from loading the cold materials to the completion of pouring molten iron is known as the charging phase.
Melting Phase:
The period from the completion of pouring molten iron to the complete melting of all furnace materials is termed the melting phase, constituting approximately 30-50% of the total smelting time.
Refining Phase:
From the completion of melting to the deoxidation process (in-furnace deoxidation) or steel tapping (out-furnace deoxidation), this period is referred to as the refining phase.
Deoxidation and Steel Tapping:
In practical operations, these phases often overlap and cannot be strictly separated.
Open hearth process of making steel
The source of heat is different to converter steelmaking, blast furnace gas or producer gas, heavy oil supplies heat in open hearth steelmaking. Heat exceeds energy barrier of reation exactly and then trigger chemical reaction of this process.
When making steel process starts, loaded fuel is burnt with conducted hot air, maximum temperature can reach 1800℃ approximately during burning process. Melting point of iron is 1535℃ and melting point of steel is lower than iron. From this point, we can see that combustion temperature is higher than melting point of iron or steel. Therefore, furnace materials can be melted promptly under this temperature. When it burns to a certain extent, some of pig iron melted generates ferrous oxide and it reacts with impurities in pig iron such as Si, Mn. Then, generates slag. What’s more, limestone can also react with P, S and any other impurities to generate calcium phosphate and calcium sulphide. And they become slags. Moreover, carbon monoxide is produced by chemical reaction between carbon and small amounts of oxygen under ignite condition. Making steel finished.
Consummate
As long as people do things are not perfect, whatever it is. Open hearth steelmaking as well as. It has some approach to consummate. Next, we will introduce briefly.
Using oxygen-reinforced materials to combust
For example, oxygen-rich flame. It increases temperature of flame and reinforces heat exchange inside of furnace. However, unfortunately, steelmaking process doesn’t change substantially;
Oxygen blowing to molten pool directly
Generally speaking, it has three approaches: furnace door oxygen blowing, top oxygen blowing and embedded deep oxygen blowing. Including, top oxygen blowing is the most common approach. This approach blows oxygen to molten pool from top position directly, oxygen replaced a lot of ores and makes C-O reaction release heat. Thus, it accelerates melting of furnace materials and oxidizing of impurities, improves dynamics condition of molten pool’s reaction prominently. Moreover, it shortens time of steelmaking. At present, it becomes main approach.
Conclusion
In conclusion, this process still used in India and some regions of Ukraine. The Open Hearth Process, despite its unassuming demeanor, remains a cornerstone in the edifice of industrial progress. Its legacy endures, echoing through the corridors of time, reminding us that sometimes, the most enduring solutions arise not from grandiose innovations but from the steady refinement of essential processes.
