Why?

Faced with Meng Qingyu's doubts, Zheng Zhendong also wanted to know the answer.

Looking at Zheng Zhendong, who was also puzzled, Wu Jinjin pondered for a while, and then did not give a direct answer, but asked instead: "Do you know the difference between ironmaking and steelmaking?" ”

"Yes, we learned it when we were in school!" Zheng Zhendong nodded, and while answering the question, he remembered the knowledge he had learned in school.

Before the Industrial Revolution, people preferred to use pure iron, and at this time, pure iron was generally calcined iron.

The use of pure iron is very rare nowadays, and the reason why this is so is because people have found a better material, which is carbon steel.

The difference between cast iron and carbon steel is the carbon content, generally speaking, cast iron has a high carbon content, and steel has a low carbon content.

The process of turning from cast iron to steel involves later converters and open hearths, so let's take a look at this process.

In fact, there are actually two routes from iron to steel, one is to start from cast iron, since the carbon content of cast iron is high, then we can find a way to reduce the carbon content of cast iron.

There is also a way to start from pure iron and obtain steel by increasing the carbon content in pure iron.

In fact, since the West first used pure iron, in the attempt to make steel, the latter route was taken first.

In fact, in the forging of iron, due to the different carbon content of the iron itself, coupled with the changes in manufacturing and heat treatment processes, humans were able to make steel by chance during the long Iron Age.

Of course, at that time, human beings were not aware of the influence of carbon content on the strength of iron-based alloys, so whether or not steel could be made completely depended on character and experience.

In order to refine the ferroalloy with better strength, the ancients also prayed to the gods and worshiped the Buddha, and used everything, and even sacrificed the sword to people.

In fact, those famous swords in ancient times should be carbon steel from today's point of view.

Historically, the first type of steel produced on a conscious scale was the so-called Damascus steel.

In the same way that Arabic numerals were not invented by the Arabs, Damascus steel actually originated in India as well.

Due to the characteristics of the Oriental smelting technology, this steel preparation method takes the route of cast iron. The Indians first smelted cast iron, then repeatedly heated and cooled it to reduce the carbon content, and finally got a steel with 1.5% carbon content, which is actually a cast steel.

Damascus steel was adopted by the Arabs as an excellent weapon and gradually spread to Europe. This was around the 7th century AD.

Damascus steel is civilized because of its unique pattern, but in fact, this is due to the lack of smelting technology.

The cast steel smelted by the Indians was called Uzi steel, and the Arabs bought steel ingots from the Indians and used them to make weapons.

Due to the large variation of the carbon content of Uzi steel, different steel ingots are repeatedly folded and forged, resulting in random patterns on the surface of the weapon.

In medieval Europe, because they had not yet mastered the technology of casting iron, they used another process to make steel, that is, carburizing, adding carbon to form steel on the basis of pig iron at the time of forging, which is similar to today's low-carbon steel.

Of course, steel is very expensive to make, and the price of steel was very high back then, so on many weapons, only the blade part is steel, and the other part is iron.

It can be seen that before the industrial revolution, the efficiency of steelmaking was very low, whether it was forging or carburizing, it was intermittent operation, and it was impossible to carry out continuous production.

All this changed during the Industrial Revolution, when steelmaking furnaces evolved from churning furnaces to open-hearth furnaces, and converters completely created the visible now, before the Industrial Revolution, the efficiency of steelmaking was very low, whether it was forging or carburizing was intermittent operation, and it was simply impossible to carry out continuous production.

All this changed during the Industrial Revolution, when steelmaking furnaces evolved from churning furnaces to open-hearth furnaces, and converters completely created the current steel industry.

Let's first talk about the traditional mixing method, using coke oven ironmaking, iron generally contains 1% silicon, in order to further obtain steel, it needs to be refined, generally speaking, refining is divided into two parts, one is to oxidize silicon, and the second step is to oxidize the carbon in iron.

In this process, the first furnace shape used by humans was a reflex mixing furnace. Through this process, the carbon content of steel can be controlled at about 0.5%-1.2%, and this technology has matured in 1850, and the melting temperature of the mixing furnace can reach 1400C.

In the 18th century, iron was added to the furnace and charcoal was burned to create a high temperature in the furnace.

The air enters in two parts, the hot air enters from the air duct, which is used for charcoal combustion, and there is a cold air intersection at the top of the furnace, and the cold air enters as an oxidizing medium to oxidize the silicon and carbon in the cast iron.

However, as the iron is purified, the melting point increases, resulting in the solidification tendency of the molten iron, so it needs to be stirred manually, so it is called a churning furnace.

On the basis of the mixing furnace, the addition of heat storage technology forms the current open-hearth furnace.

Thermal storage technology was first proposed by the German Siemens brothers in 1856 (these two Siemens are not the Siemens we are familiar with).

The so-called heat storage is to use a part of the heat storage body, generally non-silicate materials, to realize the heat exchange between furnace gas and hot air, saving the consumption of hot air energy, due to the limitation of temperature resistance of heat storage materials, heat storage technology was first applied to the glass industry, because the glass melting temperature is not high.

But around 1867, this technology was used by the Frenchman Martin for steelmaking, and finally evolved into the current open-hearth, due to the use of heat storage for heat exchange, the temperature of the open-hearth furnace can reach about 1700C, this temperature has reached the melting point of steel, so the open-hearth furnace no longer needs to be stirred, and at the same time smelting steel with lower carbon content is also called possible.

The structure of the Martin-Siemens open-hearth furnace is like this, the four lattice below are the heat storage body, two by two, the flue gas in the furnace is first heated by the first group of heat storage bodies, but the heat storage body temperature reaches the requirements and the flue gas in the furnace is passed into the other group of heat storage bodies.

At this point, air passes through the already heated regenerator, the air is preheated, and the regenerator cools. Then the gas furnace is switched, and the above process is repeated, and the air is indirectly heated by flue gas. Around the same time, another method of steelmaking began to gain popularity, and eventually continues to be used today: converter steelmaking.

Converter steelmaking is a very interesting topic, and here we will analyze the process from the perspective of reaction engineering.

First of all, let's do a heat accounting, there are two sources of heat input in this system: fuel combustion and heat release, and the other is oxidation reaction, because the reaction between air and carbon is the process of releasing heat.

What are the uses of this heat, first of all, the heat is needed to melt the iron, and the other is to heat the air and disperse it in the furnace.

Ironmaking and steelmaking are both very common processes, steelmaking mainly uses oxidation reactions, and ironmaking mainly uses oxidants to remove impurities such as sulfur and phosphorus.

Ironmaking is to reduce iron from ore with reducing agent: Fe2o3+3co=2Fe+3co2, and the main raw materials: iron ore, coke, limestone, and air.

Main equipment: blast furnace

Steelmaking is the oxidation of excess carbon from pig iron with an oxidant: C+O2=CO2.

Main raw materials: pig iron, oxygen, appropriate amount of slag material (quicklime), oxygen absorber

The main equipment is: converter steelmaking (for example), electric arc furnace steelmaking, and open-hearth steelmaking

Steelmaking process

Mining (obtaining iron ore) ---- beneficiation (crushing and magnetic separation of iron ore into iron concentrate) --- sintering (sintering iron concentrate powder into sinter with a certain strength and particle size) --- smelting (transporting the sinter to the blast furnace, and reducing the sinter to molten iron and desulfurization with hot air and coke) --- steelmaking (dephosphorizing the molten iron with high-pressure oxygen in the converter and removing inclusions and turning it into molten steel) --- refining (further dephosphorization and removal of inclusions, Improve purity) --- continuous casting (casting molten steel into a continuous casting billet with a certain shape in the hot state) --- rolling steel (rolling the continuous casting billet into various types of steel required by users, such as plates, wires, pipes, etc.).

Difference Between Ironmaking and Steelmaking

1. The raw materials are different. The raw materials for ironmaking are iron ore, coke, etc., and the raw materials for steelmaking are pig iron and scrap steel.

2. The equipment is different. Generally, the equipment used for ironmaking is a blast furnace, and the equipment used for steelmaking is a converter, electric furnace, etc.

3. The process is different. Ironmaking is the upstream of steel production, and the process is different. Ironmaking is the upstream process of steel production, and the pig iron obtained from ironmaking is the raw material of the steelmaking process, that is, ironmaking comes first, and steelmaking comes later.

4. The products are different. The product of ironmaking is pig iron (molten iron) or cast iron, and the product of steelmaking is steel (note: pig iron becomes steel after decarburization and other treatments, and the difference between steel and steel is that the carbon content is different).

To sum up: steelmaking and ironmaking are two stages in steel production, generally iron is made first, then further steelmaking, and finally various steels are obtained.

If the process of producing steel is likened to egg fried rice, then ironmaking can be seen as the process of steaming rice, and steelmaking is the process of taking the finished rice and stir-frying it.

Thinking of this, Zheng Zhendong simply repeated what he had learned.

"You're right." Wu Jinjin nodded affirmatively, and then said in a gloomy tone: "Our steel plant has neither an open hearth furnace, but also a converter, so we can't make steel at all, we can only make iron!" ”

Zheng Zhendong couldn't help but be a little surprised, and hurriedly asked, "There is no open hearth?" How so? I know we don't have a converter, why don't we even have an open-hearth? ”

Wu Jinjin sighed: "Our factory has no technology now, and you also know that the relationship between our country and Western countries is not good, so they impose a technological blockade on us, and we can't get advanced technology."

In addition, we are short of funds and can't afford tossing and wasting at all, so for the time being, we can only make iron but not steel. ”

Zheng Zhendong nodded when he heard this, and then sighed as well, thinking about seeing if he could change this status quo if he had the opportunity in the future.

The three chatted a few more words, and Zheng Zhendong saw that the time was not early, so he said: "Xiao Meng, when you have time on the weekend, call Lao Liu, let's get together then!" ”

Meng Qingyu nodded and said, "Well, okay Brother Dong, when I get off work in the evening, I'll tell Lao Liu!" ”

The three of them stood up and walked to the sink to clean the lunch box.

Then Zheng Zhendong, accompanied by Wu Jinjin and Meng Qingyu, walked to the canteen exchange office to exchange some meal tickets, and then walked out.

After leaving the cafeteria, Zheng Zhendong patted Meng Qingyu's arm with a smile and said, "Okay, Xiao Meng, I'll go to work first, let's talk when we're free!" ”

"Okay, Brother Dong, then I'll go to work too, let's talk back, and when I'm free, I'll go to the engineering headquarters to see you!"

After saying this, Meng Qingyu nodded, and then walked to the east with the lunch box.