KR100391908B1 - Method of Manufacturing Ultra Low Carbon Steel for Supper Extra Deep Drawing Quality - Google Patents

Abstract

The present invention relates to a method for producing ultra-low carbon steel for deep processing excellent in cold work, the object is to enable the control of phosphorus and nitrogen without the need for additional equipment for deep work in cold work It is to provide a way to obtain ultra low carbon steel.

The present invention for achieving the above object in the method for producing ultra-low carbon steel, carbon 3.0-5.0% by weight, silicon 0.05-1.0% by weight, manganese 0.05-1.0% by weight, phosphorus 0.06-0.20% by weight, sulfur 0.002- Using molten iron containing 0.05% by weight, the amount of iron in the converter was controlled in the range of 2500-4000 Nm ³ and soft blown to reduce the phosphorus content to 0.050% or less, and Ar gas was supplied from the lower part of the converter to supply nitrogen. Conducting primary scavenging controlling to 15 ppm or less; In addition, after the first blow, the molten steel is reloaded into the decarburization furnace to control the amount of acid in the range of 10000-14000 Nm ³ , followed by hard blowing to carry out the second blow to reduce the phosphorus content to 0.006% or less with decarburization. The present invention relates to a method for producing ultra-low carbon steel for deep processing, which is excellent in workability in a cold state.

Description

Method of Manufacturing Ultra Low Carbon Steel for Supper Extra Deep Drawing Quality}

The present invention relates to a method for manufacturing a deep-low carbon steel for deep processing, and more particularly, to minimize the content of carbon, phosphorus, sulfur, nitrogen, etc., elements in the steel, so that no cracks occur during processing in cold state, cold state It relates to a method for producing ultra-low carbon steel showing excellent workability at.

In order to manufacture ultra-low carbon steels for deep processing in the conventional steelmaking process, it is necessary to minimize the impurity elements existing in the steel. Therefore, in the converter process, phosphorus and nitrogen are reduced, and carbon and nitrogen are simultaneously controlled by vacuum treatment in the secondary refining process. I had a process to do it.

On the other hand, since cracks generated during processing mostly occur in segregation areas or non-metallic inclusions generated during casting, phosphorus and non-metallic inclusions generated during deoxidation are removed. What is needed more than anything. However, in the prior art, there was a limit in removing phosphorus only by the converter process, and thus, a process of operating in the converter after removing phosphorus using a pretreatment process was selected. In order to use this pretreatment process, a separate facility is required.

In the conventional ultra-low steel manufacturing technology, the process of refining molten iron and gaseous oxygen into molten iron before removing the molten iron into the molten iron prior to charging the molten iron into the converter, i.e. Was producing through. Delineation operation using the molten iron preliminary treatment is a very useful method to lower the phosphorus component in the molten steel to 100ppm level or less.

However, such a conventional method has a severe temperature drop in the charter preliminary treatment step, and thus has a burden of temperature increase during converter refining. In addition, after performing the pretreatment, the nitrogen level of the molten iron is about 0.0030% level, and there was a problem that it is difficult to stably reach the target of 0.0020% or less only by controlling in the post-process.

Accordingly, the present inventors have repeatedly studied and experimented to solve the problems of the prior art, and based on the results, the present invention proposes a control of phosphorus and nitrogen without requiring additional equipment. It is possible to provide a method for obtaining ultra-low carbon steel for deep processing which is excellent in workability in a cold state.

1 is a process diagram briefly showing a converter work process according to the present invention

Figure 2 is a graph showing the content of P according to the blowing time (blowing time)

3 is a graph showing the content of N according to the blowing time

Figure 4 is a graph showing an example of the amount of shedding and lance height adjustment during the first blow according to the present invention

Figure 5 is a graph showing an example of the amount of shedding and lance height adjustment when blowing by the conventional method

Figure 6 is a graph showing an example of the amount of shedding and lance height adjustment during the second blow according to the present invention

In order to achieve the above object, the present invention provides a method for producing ultra-low carbon steel in which carbon is controlled to 0.0020% by weight or less, phosphorus to 0.008% by weight, sulfur to 0.008% or less, and nitrogen to 0.0020% by weight or less. By using molten iron containing -5.0% by weight, 0.05-1.0% by weight of silicon, 0.05-1.0% by weight of manganese, 0.06-0.20% by weight of phosphorus and 0.002-0.05% by weight of sulfur, the amount of acid in the converter is in the range of 2500-4000Nm ³ And primary blowing to control the nitrogen to 15 ppm or less by reducing the phosphorus content to 0.050% or less, and supplying Ar gas from the lower part of the converter; In addition, after the first blow, the molten steel is reloaded into the decarburization furnace to control the amount of acid in the range of 10000-14000 Nm ³ and hard blowing to reduce the phosphorus content to 0.006% or less with decarburization. It relates to a method for producing ultra-low carbon steel for deep processing excellent in workability in the cold state characterized in that to carry out.

Hereinafter, the present invention will be described in detail.

As described above, the phosphorus component in the steel is segregated during the solidification process, causing cracks in the process of processing the material after rolling. In other words, in steels requiring deep processing, if the phosphorus content in the steel is high, the cracking is most likely to occur. Therefore, it is necessary to minimize the phosphorus content in the steel, but it is difficult to obtain stably less than 0.008% required for such steels as a general operation technique. Therefore, in many cases, the present invention is manufactured through a charter preliminary treatment process, but in the present invention, a phosphorous content of 0.008% or less can be obtained through converter refining without charter preliminary treatment.

In the present invention, as shown in Fig. 1, the phosphorus content is primarily reduced by using solid oxygen and gaseous oxygen in the converter, and the phosphorus content is lowered by tapping it again and charging it in another converter to perform the secondary treatment. In other words, by using an electric converter, which is an idle facility, as a Tallin furnace for lowering phosphorus content, the level pursued in the present invention can be obtained. In addition, for stable control of nitrogen below 0.0020%, the initial nitrogen content should be lowered. In general, the nitrogen level of molten iron is about 0.0030%. In addition, the initial nitrogen is about 0.0015%, which allows for nitrogen control.

When the present invention is divided into phosphorus control and nitrogen control, it will be described as follows.

First, the phosphorus control will be described. The level of phosphorus that can be obtained through general operation varies slightly depending on the process, but cannot be stably satisfied below 0.010%. In order to satisfy these extreme levels, as described above, in most molten iron preliminary treatment steps, the phosphorus content is reduced and converter refining is performed. At this time, the phosphorus content is about 0.025%. In the present invention, the molten iron having a phosphorus content of 0.110% level was charged into a delineation furnace, which is a converter type pretreatment container, to perform primary talin, and the process of tapping the melt was loaded again into the decarburization furnace. At this time, the phosphorus content was 0.025% after the first Tallinn, 0.006% after the decarburization was completed, which can be seen even in Figure 2 showing the phosphorus content change during the operation of Tallinn.

In addition, since the concentration of P ₂ O ₅ in slag separated from molten steel during the operation of the general converter showed 2% level, it was virtually impossible to secure stable quality due to the occurrence of double rinse during secondary refining, P ₂ O ₅ concentration in the slag was reduced amount bokrin to 1%.

Next, the nitrogen control will be described. Nitrogen present in the molten metal is present in the atom state, not in the gaseous state, and the mechanism of the nitrogen content is known by Sivet's Law as shown in Equation (1) below.

wt% [N] = kN (PN2) 1/2

That is, the nitrogen level in the molten metal has a relationship proportional to the partial pressure of nitrogen in the atmosphere gas, and to lower the nitrogen level, it is required to lower the nitrogen partial pressure in the atmosphere gas.

In general, in the early stage of blowing, the carbon in the molten iron reacts with oxygen supplied to form a CO gas, so the partial pressure of nitrogen in the furnace atmosphere is relatively low, and the generated CO gas is released to the outside of the furnace to absorb and release [N] in the steel. Therefore, the initial nitrogen of the blowing is reduced. However, since the amount of gas generated as the decarburization reaction decreases at the end of the blowdown becomes smaller, the partial pressure of CO gas in the furnace atmosphere gas is lowered and the overall gas pressure is lowered, thereby increasing the possibility of introducing air from the outside. Thus, nitrogen, which occupies 79% of the atmosphere, can easily be picked up in molten steel and it is virtually impossible to prevent the pickup of nitrogen. However, in order to reduce nitrogen pick-up at the end of the blowdown, the present invention measures carbon concentration and temperature at a time when the carbon concentration in molten iron is 0.30% or more and 0.70% or less after the blowdown period. In order to increase the pressure, in order to minimize the inflow of external air by inputting a subsidiary material advantageous for gas generation, the pickup amount was about 5ppm. Therefore, minimizing the nitrogen content in the molten metal by lowering the nitrogen level in the molten iron has become an important part of the ultra-low nitrogen steel.

Nitrogen content in molten iron is generally 20-30 ppm. Since the denitrification rate during converter conversion is almost constant, the nitrogen during the drilling is reduced to about 10 to 15 ppm, but as described above, the molten steel nitrogen is 15 to 20 ppm at the completion of the drilling by the end of the nitrogen pickup. In addition, considering the amount of absorbed by the atmosphere during the tapping, the nitrogen of the final product is about 25ppm level, it is impossible to control the ultra low nitrogen steel.

In the present invention, in order to control the nitrogen, agitation gas supplied from the lower part of the converter during the operation of the converter was used as Ar, and carbon dioxide was generated by oxidizing 0.5% of carbon. Therefore, as Ar gas floats, some of the nitrogen in the molten iron is removed, and the generated CO gas also removes nitrogen. As a result, when the decarburization furnace was charged, the nitrogen level was reduced to 15 ppm, and the nitrogen level during the blowing was 7 to 10 ppm, and the nitrogen at the completion of the blowing was stable to 13 to 15 ppm. It can also be seen by looking at Figure 3 shown.

The following describes in more detail the converter operation technology applied to the present invention. The converter operation technology applied to the present invention can be divided into two types: primary blowing operation (tallin operation) and secondary blowing operation (decarburization operation).

First, the primary blowing operation is to selectively react silicon and phosphorus using an appropriate amount of slag and to perform the operation in the manner as shown in FIG. 4, for example, to suppress the oxidation of carbon as much as possible, which is the same as that of FIG. 5. It can be called soft blowing compared to existing operating standards. The reason for such soft blow is that when gaseous oxygen supplied through oxygen lance is supplied to molten iron, that is, when a cavity is formed on the surface of molten iron, decarburization is performed together with Tallinn, so that molten iron is removed after desalination operation. This is because the slag swells when it deteriorates and the workability is significantly deteriorated. Also, when carbon is oxidized, an adverse condition for Tallinn is formed by the temperature rise.

In conclusion, it is preferable to control the amount of frosting in the range of 2500-4000Nm ³ for the primary scavenging, and in order to obtain a better effect, the soft blowing of the cavity ratio (L / L ₀ ) of the molten steel in the hot water surface is 0.05 or less. (soft blowing) is good. In addition, it is preferable to supply Ar gas from the lower part of the converter in order to control nitrogen to 15 ppm or less during the first blow.

Next, the secondary blowing operation is preferably performed for example, the type of operation shown in FIG. This is somewhat different from the conventional standard shown in FIG. 5 and this difference is due to the difference in components of the molten iron. In other words, since the content of silicon contained in the molten iron is greatly different from that of general molten iron, the molten iron is generally difficult to form slag in the initial converter, so that a so-called spitting phenomenon occurs in which molten iron is ejected out of the converter. Because.

In conclusion, it is preferable to reload the molten steel into the decarburization furnace after the first blow to control the amount of acid in the range of 10000-14000 Nm ³ , and to obtain a better effect, the cavity ratio of the molten steel (L / L ₀ ) is 0.5 at the hot water surface. Hard blowing of -0.7 is recommended.

In addition, since the CO generation is reduced after the middle stage of the secondary blow, there is a problem that the N component in the air is mixed because the pressure in the converter is lowered, to prevent this, by continuously injecting solid oxygen such as iron ore, sintered ore after the middle stage It is desirable to prevent the rise of nitrogen by maintaining the pressure in the decarburization furnace above a certain level.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example

A molten iron containing 4.0% by weight of carbon, 0.07% by weight of silicon, 0.5% by weight of manganese, 0.11% by weight of phosphorus and 0.01% by weight of sulfur was charged into a 300-ton converter.

After the injection, the primary drilling was carried out by injecting Ar gas by the method as shown in FIG. 4, and then the tapping was carried out to another converter, and the secondary drilling was performed by the method as shown in FIG. 6. The pressure in the converter was kept constant. Subsidiary material injection in such an operation was performed similarly to the conventional method. Four operations were conducted in this manner, and the components of the obtained steel were analyzed, and the contents of carbon, phosphorus, sulfur and nitrogen are shown in Table 1 below.

In addition, after pouring molten iron of the same component into the converter, it was blown by the method similar to FIG. 5, and other conditions were performed on normal conditions. Four operations were conducted in this manner, and the components of the obtained steel were analyzed, and the contents of carbon, phosphorus, sulfur and nitrogen are shown in Table 1 below.

Carbon (ppm) Phosphorus (ppm) Sulfur (ppm) Nitrogen (ppm) Conventional example Primary 22 100 50 22 Secondary 21 90 50 23 3rd 24 120 40 20 4th 20 120 40 22 Inventive Example Primary 20 60 50 18 Secondary 19 50 40 14 3rd 20 60 40 16 4th 17 60 40 18

As can be seen in Table 1, the invention examples satisfying the conditions of the present invention showed a very good removal effect on the phosphorus and nitrogen while showing the same level of carbon and sulfur content than the conventional example.

According to the present invention as described above, it is possible to obtain carbon steel minimized phosphorus and nitrogen without the need for additional equipment in the production of ultra-low carbon steel, and when applied to deep processing, the effect of showing excellent workability in cold state Is provided.

Claims (3)

In the method for producing ultra-low carbon steel, controlled to less than 0.0020% by weight, less than 0.008% by weight of phosphorus, less than 0.008% by weight of sulfur, and less than 0.0020% by weight of nitrogen, Using a molten iron containing 3.0-5.0% by weight of carbon, 0.05-1.0% by weight of silicon, 0.05-1.0% by weight of manganese, 0.06-0.20% by weight of phosphorus and 0.002-0.05% by weight of sulfur, the amount of acid in the converter is 2500-4000 Nm. Controlling to ^three ranges and performing soft blowing to reduce the phosphorus content to 0.050% or less, and to carry out primary scavenging to control nitrogen to 15 ppm or less by supplying Ar gas from the lower part of the converter; In addition, after the first blow, the molten steel is reloaded into the decarburization furnace to control the amount of acid in the range of 10000-14000 Nm ³ and hard blowing to reduce the phosphorus content to 0.006% or less with decarburization. Method for producing ultra-low carbon steel for deep processing excellent in workability in the cold state characterized in that for carrying out The method of claim 1, The primary blow is a cavity (cavity) of molten steel ratio (L / L ₀₎ of 0.05 or less at the bath surface, the secondary blow is characterized in that the cavity ratio of the molten steel (L / L ₀₎ in the bath surface 0.5-0.7 Manufacturing method of ultra low carbon steel for deep processing with excellent workability in cold state The method according to claim 1 or 2, Method of producing ultra-low carbon steel for deep processing excellent in workability in the cold state, characterized in that by continuously adding solid oxygen after the secondary stage of the secondary smelting to maintain the pressure in the decarburization furnace to a certain level or more.