KR950012405B1 - Making method of dead mild steel - Google Patents

Abstract

The method comprises a step of controlling terminal carbon content below 0.045%; a step of adding one or two kinds of Mn-providing group and Si-Mn, Fe-Si separately or compositely, then degassing by Al for oxygen content to be 60-100ppm; a step of controlling molten steel temperature, remaining oxygen content etc.; and a step of continous casting by putting low carbon flux in the molten steel.

Description

Manufacturing method of soft mild steel

1 is a reference diagram showing an example of a temperature change of molten steel in each step when producing soft mild steel according to a conventional method of performing degassing treatment.

2 is a reference diagram showing an example of a temperature change of molten steel in each step when producing soft mild steel according to the present invention method which does not perform degassing treatment.

The present invention relates to a method for producing soft mild steel for use in galvanized iron wire, annealed iron wire, special nails and the like, and more particularly, to a method for producing soft mild steel without degassing treatment.

In the converter of the steel mill, the molten iron containing a large amount of impurities such as carbon is oxidized and refined to pure oxygen, and then deoxidized oxygen remaining in the molten steel, and various iron alloys and subsidiary materials are made to meet the mechanical properties required by the characteristics of the product. Put your back on the class.

Degassed mild steel oxidizes the carbon in the molten steel to 0.04% during the oxygen scavenging process in the converter process. At the same time, oxygen is blown more to decarburize less than 0.04%, or if the converter is operated at a high temperature of 1700 ℃ or higher, the melting of converter refractory proceeds rapidly, resulting in an increase in cost. Work and high temperature tapping are avoided as much as possible, but if the temperature is low, post-processing is difficult, so degassing mild steel is inevitable for high temperature tapping at about 1720 ℃, resulting in reduced converter life.

The molten steel refined by this converter process is inputted during the tapping of Al, Si-Mn-tung ferroalloys for deoxidation and component adjustment, and then decarburized to the level required by the product in the degassing and refining process, and finely adjusting the components. And temperature, dissolved oxygen, etc., suitable for continuous casting, wherein the temperature of molten steel drops by about 30 ° C during degassing.

After degassing and refining, the molten steel is cast in a continuous casting machine after fine adjustment of temperature and dissolved oxygen in a bubbling stand.

In other words, since soft tensile steel material requires low tensile strength in the product, it is necessary to lower the carbon component which has a great influence on the strength, so degassing treatment of decarburization, etc. is inevitable. Due to the high melting temperature, when the molten steel is produced in the converter, the work must be performed at a high temperature of more than 1700 ° C. As a result, the temperature of the degassed mild steel material as well as the shortening of the converter refractory life, which occupies the largest part in the manufacturing cost, are the It is higher than about 40 ℃, and there is a problem such as load weight of the degassing treatment due to degassing treatment.

Therefore, there is a demand for a method of producing soft strength without degassing within a range that does not affect the quality of the material.

An object of the present invention is to provide a method capable of producing soft mild steel that does not deteriorate compared to conventional degassed mild steel even if degassing is not performed by meeting the above requirements.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention provides a method for producing a soft mild steel, the step of adjusting the final carbon amount in the converter to less than 0.045%, and then tapping; Adding Mn source and Si source so that Mn / Si ratio in molten steel is 3.0 or more during tapping, and then adding Al to deoxidize the amount of oxygen in molten steel to be 60-100 ppm; Adjusting the temperature, dissolved oxygen, and other components of the molten steel in a conventional manner by dividing it into a before and after bubbling step; And it relates to a method for producing a soft mild steel comprising a continuous casting step in a conventional method.

In the case of the present invention, in the case of continuous casting in a continuous casting machine it is preferable to add the chaff hush in the tundish during casting.

Hereinafter, the present invention will be described in more detail.

Since the tensile strength is too high when the amount of end carbon in the converter is 0.045% or more, the amount of end carbon is preferably limited to 0.045% or less, and more preferably 0.038% or less.

In the present invention, while eliminating the degassing for the purpose of decarburization, soft carbon steels having properties similar to those of conventional steels can be obtained while maintaining carbon content in mild steels higher than conventional steels, and lowering the Mn content in steels compared to conventional steels. It can be.

To this end, the Mn source and Si source are input during the tapping of the ladle in the converter, and the input amount is preferably set such that the Mn / Si ratio is 3.0-20.

And, as the Mn source can be used alone or in combination with Fe-Mn, Si-Mn and pure Mn, the Si source can be used alone or in combination with Fe-Si, Si-Mn and pure Si. have.

The reason for introducing the Mn source is for deoxidation of molten steel and adjustment of the Mn component in the molten steel, and the reason for adding the Si source is for stable casting by improving oxygen content and castability in the molten steel.

When the Mn / Si ratio is 3.0 or less in the molten steel when the Mn source and the Si source are added, the composition of the oxide formed during casting has a high melting point range and blackout occurs in the cast steel, or the high melting point oxide is formed in the cast steel. If the Mn / Si ratio is 20 or more, the Mn content in the steel increases, which makes it easy to be a hard mild steel. Therefore, the amount of the Mn source and the Si source is increased in the molten steel. It is desirable to limit the Mn / Si ratio to 3.0-20.

After adding the Mn source and the Si source as described above, Al is added so that the amount of oxygen in the molten steel is 60-100 ppm.

At this time, if the dissolved oxygen amount is less than 60ppm, Al ₂ O ₃ , which is a high melting point inclusion, is formed, which causes nozzle clogging during casting, and if it is more than 100ppm, defects such as pinholes are generated on the surface of the cast steel, resulting in poor surface condition. The amount of Al added is preferably limited to a dissolved oxygen amount of 60-100 ppm.

In this converter step, the temperature and components and dissolved oxygen amount are more precisely adjusted in detail in the bubbling stand after the first adjustment of the components and the dissolved oxygen amount together with the temperature. That is, in the converter stage, it is difficult to precisely adjust the temperature, components and dissolved oxygen amount necessary for continuous casting. In the bubbling stand, the above conditions are finely adjusted. Adjust temperature, dissolved oxygen and other ingredients For example, in the bubbling stand, mainly Fe-Mn is added to adjust the composition, and the other components are adjusted as in the converter, and for the temperature adjustment, the bubbling time and the flow rate are adjusted. What is necessary is just to adjust to the temperature made into. In addition, dissolved oxygen amount is normally dropped to 10 ppm by adding Al.

When continuously casting the molten steel prepared as described above in a continuous casting machine, it is preferable to inject a low carbon-containing flux on the molten steel received in the tundish, the amount of the input is preferably limited to less than 3kg / ton-molten steel.

The reason why the low-carbon-containing flux is added to the molten steel is not only to insulate the molten steel and to prevent molten steel reoxidation, but also to inhibit carbon pick-up so that the carbon content of the final cast does not increase by more than 0.04%.

To this end, in the present invention, it is more preferable to use the husk chaff as a low carbon-containing flux instead of the conventional charcoal chaff.

Soft mild steel that can be more preferably produced according to the present invention includes a steel containing C: 0.04% or less, Si: 0.05% or less, Mn: 0.20% or less by weight.

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

EXAMPLE

As shown in Table 1, in the case of the present invention, the final carbon content is 0.035% in the converter, the end temperature is adjusted to 1690 ° C., Si-Mn 50Kg, Fe-Si 70Kg, and Al are added during tapping. The process was not degassed and the uniformity of molten steel temperature and components was divided into pre-bubbling and post-bubbling at the bubbling stand to adjust the temperature, dissolved oxygen and components in the molten steel and then cast in a continuous casting machine. In casting, huh chaff was added to the tundish. On the other hand, in the conventional method, degassing treatment was performed in a degassing facility as shown in Table 1 below, and carbonized rice husk was added to the tundish. In this case, Fe-Mn of 2Kg / ton-molten steel is introduced during desorption and decarburization is carried out in a degassing facility under a vacuum of 50torr or less, and then Fe-Si of 0.7Kg / ton-molten steel and Fe of 0.7Kg / ton-molten steel Al of -Mn and 0.2Kg / ton-molten steel was added.

The composition and tensile strength of the mild steel prepared as described above were investigated, and the results are shown in Tables 2 and 3, respectively.

In addition, the temperature change in each process was observed in the conventional method and the present invention method, and the results are shown in FIGS. 1 and 2, respectively.

TABLE 1

TABLE 2

TABLE 3

As shown in Table 2 and Table 3, the present invention is included in the composition range of the soft mild steel, it can be seen that the mechanical properties also have a level equivalent to that produced by the conventional method.

On the other hand, as shown in Figs. 1 and 2, in the case of the present invention method (Fig. 2), the temperature of the converter end point is 1690 ° C., and the conventional method considering the temperature (30 ° C.) dropped during degassing treatment ( It can be seen that the end temperature of 1 degree) is 30 ° C lower than the end temperature of 1720 ° C, which means that it is possible to obtain an effect out of the ultra high temperature converter end temperature (temperature at which refractory loss rapidly progresses to 1700 ° C or more). In the converter process, the end point temperature is reduced by 30 ° C, which can reduce the amount of pure oxygen used by 150 Nm ³ .

As described above, the present invention can produce soft mild steel having almost the same mechanical properties as conventional soft mild steel subjected to degassing even without degassing, thereby extending refractory life as well as degassing. The non-treatment will have the effect of reducing the manufacturing cost.

Claims (2)

In the method for producing a soft mild steel containing by weight%, C: 0.04% or less, Si: 0.05% or less, Mn: 0.20% or less, after adjusting the amount of end carbon in the converter to 0.045% or less, step; Si-Mn and Fe-Si added alone or in combination with one or more selected from the group of Mn sources consisting of Si-Mn, Fe-Mn and pure Mn so that the Mn / Si ratio in molten steel is 3.0-20 during tapping After that, adding and deoxidizing Al so that the amount of oxygen in the molten steel becomes 60-100 ppm; Adjusting the temperature, dissolved oxygen and other components of the molten steel in a conventional manner by dividing the bubbling stand before and after bubbling treatment; And casting a low carbon-containing flux below 3 Kg / ton-molten steel on the molten steel received in a tundish, followed by continuous casting in a conventional manner. The method of claim 1, wherein the flux is inverse chaff.