KR930000842B1 - Process for making high oxygen rimmed steel - Google Patents

Abstract

The high oxygen rimmed steel is prepared by (a) tapping nonoxidatively molten steel containing 0.1 wt.% carbon, after converter blow refining at more than 1600 deg.C, (b) decarburizing and degassing molten steel to less than 100 ppm of carbon concentration and more than 30 ppm of free oxygen, (c) adding heat-retaining materials containing 3.0 wt.% carbon in tundish, and (d) putting molten steel into the mold with material containing less than 1.0 wt.% carbon, and casting continuously.

Description

Method for producing high oxygen limped steel.

1 is a relationship diagram of C-O showing whether a pin hole is generated.

The present invention relates to a method for manufacturing a limmed steel by a continuous casting method, and more particularly, to a high-oxygen rim steel having excellent quality without generating pinholes by continuous casting under operating conditions in which CO bubbles will not be generated. It relates to a method of manufacturing.

In general, a rimmed steel is manufactured by a coarse method, and such a rim steel forms a rim layer upon solidification, so that the surface is beautiful and the workability is good, and thus a thin plate and wire rod are required. It is widely used for general structures, and in particular, low carbon rim steel is widely used for press and deep drawing because of its good viscosity.

That is, in the steel of the ingot is high in [O] _f (Free Oxygen) in the molten steel, carbon in the molten steel is combined with the above [0] _f during solidification to generate bubbles of CO gas. Since the CO bubbles are discharged out of the molten steel while stirring the molten steel, a cast product that does not generate pin holes can be obtained, thereby obtaining a beautiful surface and a soft material that is characteristic of the rim steel. However, in the situation where most steel materials have recently been reduced in manufacturing cost through mass production by the continuous casting, the production of rim steel by a recipe that inevitably undergoes the process of ingot is inexpensive in terms of production and manufacturing process, so the rim It is difficult to obtain the quality of the steel, but the corresponding limd steel, which manufactures the corresponding material by continuous casting, has been replaced.

However, in the continuous casting method, since the cold cooling is inevitable during continuous casting, CO bubbles cannot be discharged during solidification, which causes CO holes to cause pinholes in steel.

Therefore, the rimmed steel corresponding to deoxidizing the molten steel by adding Al or Si or the like of steel deoxidizer for the pinholes prevented during continuous casting and prevent pinhole generation by the molten steel to be kept low [0] _f.

However, in the limbed steel, Al and Si injected into molten steel produce Al ₂ O ₃ and SiO ₂ , which are nonmetallic inclusions, and a part of them remain in molten steel and exist as solid solution Al and Si in molten steel. The Al ₂ O ₃ and SiO ₂ non-metallic inclusions thus produced cause processing cracks during processing, and the solid solution Al inhibits workability by hardening steel by miniaturizing particles, and the Si causes adverse effects on plating degradation. There is this.

Therefore, the present invention is the operating condition that does not generate CO bubbles, that is, the deoxidation tapping without the addition of deoxidizer such as Al and Si during the tapping of the converter, after producing ultra-low carbon steel while maintaining the high oxygen state in the furnace refining process By continuous casting using a material with low carbon content so that carburization does not occur during the performance, it is intended to manufacture high-oxygen rim steel with high quality without generating pinholes. EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

According to the present invention, the molten steel subjected to vacuum degassing and bubbling treatment after the converter is injected into a continuous casting mold using materials such as mold oil through a tundish into which a material such as a heat insulating material is injected into the rim. In the method for producing a de-steel, the carbon content is 0.1wt% or less, the molten steel which has been converted to the molten steel temperature of 1600 ℃ or more is not deoxidized, the carbon concentration is 100ppm or less using a vacuum degassing apparatus, [0] After decarburization and deoxidation treatment so that _f is 30ppm or more, it is injected into a continuous casting mold using a material having a carbon content of 1.0wt% or less through a tundish in which a material having a carbon content of 3.0wt% or less is injected and continuously It relates to a method for producing high oxygen limmed steel by casting. Hereinafter, the reason for numerical limitation will be described in detail.

In the converter blasting, the carbon content after the churning to be less than 0.1wt% in order to facilitate the removal of carbon (C + O → CO (gas)) in the vacuum degassing apparatus because it is impossible to manufacture very low carbon steel in the converter, In order to enable continuous casting, it is desirable to set the molten steel temperature to 1600 ° C or higher in consideration of the theoretical solidification temperature (1530 ° C).

Further, when tapping is not input a deoxidizer such as Al and Si to keep [0] _f 300ppm or more is easy to carbon removed in the next step of vacuum degassing process, as [0], a state in which _f is a saturated Although it is preferable to hold | maintain, a deoxidizer, such as Al and Si, may be added for _f adjustment.

The vacuum degassing treatment is divided into decarburization and deoxidation adjustment, and during decarburization, it is preferable to secure a vacuum in the early stage and to maximize the reflux of molten steel so that the carbon concentration is 100 ppm or less after decarburization. [0] _f concentration is strictly to the deoxidation with Al and Si, it is preferred to keep [0] _f 300ppm or more, specifically with respect thereto as follows.

1 is a relation diagram of CO indicating whether pinholes occur at 1600 ° C and Pco = latm, and CO bubbles calculated from ΔG (standard free energy) =-RTlnK in the formula [C] + [O] = CO (gas) The generated threshold value and the measured CO bubble generation threshold value are shown.

Where log K (= log Pco / ac.ao) = 1160 / T-2.003 (K: equilibrium constant, Pco: Co partial pressure, ac: [C] activity, a ₀ = [O] activity, T : Absolute temperature)

△ G = -5300-9.17T

log fc = 0.298. [% C] (activity coefficient for fc: [C])

log f _{0 =} -0.421 [% O] (activity coefficient of f ₀ : [O])

As shown in FIG. 1, it can be seen that the calculated CO bubble generation limit value and the measured CO bubble generation limit value do not coincide with each other. The present invention is proposed based on the measured CO bubble generation limit value. .

In order to obtain the characteristics of the limped steel, it can be seen that the condition that [C] + [O] → CO (gas) reaction does not occur when the content of at least 30 ppm is [O] _f should be less than 100 ppm in molten steel.

On the other hand, in the present invention, as an external factor for continuous casting, the content of carbon contained in materials such as thermal insulation materials put into tundish and flux used in continuous casting molds in order to prevent carbon from being carburized into molten steel to generate CO bubbles. Alternatively, it is desirable to reduce the content of carbon in materials such as mold oil as much as possible, but the carbon content in materials such as thermal insulation materials put into tundish is 3.0 wt% or less, and the flux or mold oil used in the mold The carbon content of the material is preferably limited to 1.0wt% or less. Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

In the following, the final carbon of the amount and the end oxygen of the dissolved oxygen in 1748 ℃ to the end temperature of the pretreatment and fine deoxidation and outgoing, then by using a vacuum degree of 1Torr Fe-Mn and Si and Al for deoxidation adjustment After decarburization and deoxidation, RH vacuum degassing was carried out such that [C] and [O] _f were in the amounts shown in Table 1, followed by bubbling for 2 minutes in a bubbling stand for temperature adjustment. .

After the molten steel prepared as described above is introduced into the tundish, a thermal insulating material having a carbon content as shown in Table 1 is added to the molten steel, and then into a continuous casting mold using a mold oil having a carbon content as shown in Table 1 below. Injection was carried out and continuous casting was performed.

The number of pinholes was investigated for the steel produced by casting as described above, and the results are shown in Table 1 below.

In addition, various characteristics were measured about the invention steel 1 of the following Table 1, and the measurement result is shown in following Table 2 with the general characteristics of the conventional rim | corrugated steel.

TABLE 1

TABLE 2

As shown in Table 1, the invention steel (1-4) for converter smelting, degassing and continuous casting in accordance with the present invention is within the range of 50 or less, which is the allowable number of pinholes in conventional rim steel, Comparative steel (ab) outside the scope of the invention is generated a large amount of pinhole, it can be seen that the comparative steel (C) is impossible to cast.

In addition, as shown in Table 2, the invention steel (1) has a low tensile strength of 31-32㎏ / ㎠ compared to the conventional rim-adaptive steel is excellent in the soft nitriding degree and the surface finish rate of import and rolling It can be seen that the upset failure rate indicating the groove generation rate is low, so the error rate is excellent.

As described above, according to the present invention, the quality is superior to that of the conventional rim-compliant steel, and the cost can be reduced due to the elimination of the crushing rolling process compared to the conventional rim steel.

Claims (1)

After the converter is blown, the molten steel with vacuum degassing and bubbling treatment is injected into the continuous casting mold using materials such as mold oil through the tundish into which the material is insulated. In the method of manufacturing, the carbon content is 0.1wt% or less, the molten steel is subjected to undeoxidation after the converter is blown at a molten steel temperature of 1600 ° C or higher, and the carbon concentration is 100ppm or less using a vacuum degassing apparatus and at the same time [O] _f After the decarburization and deoxidation treatment is carried out to 30ppm or more, it is injected into a continuous casting mold using a material having a carbon content of 1.0wt% or less through a tundish to which a material having a carbon content of 3.0wt% or less is injected. Method for producing high-oxygen rim steel, characterized in that.