KR950012418B1 - Making method of low hydrogen clean steel - Google Patents

Abstract

The manufacturing method improves mechanical properties such as toughness and bendability by retarding the corrosion of refractories and applying calcium silicon. The manufacturing method comprises(A) charging deoxidizers with aluminum into the converter; (B) bubbling the molten steel and slag; (C) degassing treatment under the vacuum atmosphere for 10-15 minutes.

Description

Manufacturing method of high clean thick plate material

1 is a graph showing the change in the amount of oxygen in accordance with the calcium-silicone desorbent blowing amount using the upper lance.

Figure 2 is a graph showing the hydrogen content change according to the degassing treatment time after spraying the spray material by the present invention method and the conventional method.

3 is a graph of a comparison of the defective rate by the ultrasonic flaw detection method in the present invention and the conventional method.

4 is a graph showing the sulfur concentration in the segregation portion in the present invention method and the conventional method.

5 is a graph showing the Charpy impact value at -45c in the present invention method and the conventional method.

The present invention relates to a method for removing and controlling non-metallic inclusions by using calcium-silicon (Ca-Si) blowing and degassing equipment in a converter, and producing hydrogen-removed high-clean thick plate materials by removing hydrogen. will be.

The thick plate material is formed by the rolling direction stretching of the core microcracks (CracK) and the emulsion type inclusions, microcracks of manganese, and sulfur thick segregation due to the increase of the thickness of the oxide and emulsion-based nonmetallic inclusions and hydrogen in the steel. By causing white spot phenomenon due to excessive hydrogen accumulation, it lowers the mechanical properties such as strength and fatigue resistance of steel, and also causes various defects and fractures by impact fatigue during bending and use.

Therefore, in case of thick plate material, ultrasonic flaw detection is performed to measure its defects, and it is impossible to use it in the event of a defect.

On the other hand, in order to remove the inclusions in ordinary converters can be carried out by stirring the deoxidized molten steel or by improving the deoxidation method and adjustment of the molten steel component, the removal of the inclusions using these methods is limited, even if the molten steel is properly treated The removal of inclusions in which the slag floats is limited, and even if the molten steel is properly treated, if the slag on the molten steel is not suitable for the absorption of the floating inclusions, the injured inclusions are not absorbed by the slag layer and are swept back into the molten steel circulation stream. .

Therefore, in order to reduce the amount of non-metallic inclusions and to produce high clean steel, the molten steel is treated to react with slag that is easy to absorb nonmetallic inclusions after tapping and deoxidation is completed.

On the other hand, in the thick plate material molten steel produced through converter refining, the upper ladle slag is formed by the converter slag which is inevitable inflow during tapping and the deoxidation product generated during deoxidation work during tapping, mainly CaO, SiO ₂ and AI _It consists of ₂ O ₃ and contains a small amount of FeO and MnO. The slag, by itself, has a high melting point, which leads to low reactivity and low removal rate of non-metallic inclusions, making it inefficient for clean steelmaking.

In manufacturing molten steel of conventional thick plate material, in order to reduce non-metallic inclusions and hydrogen, the deoxidizer is added at the time of tapping, and the weight ratio to the total loss lag is based on the total loss lag 3-25Kg per ton of molten steel, which is the total amount of total loss lag. Quick lime 0.7-1.2 is added during the tapping to strike the tapping flow for sufficient mixing, and the oxygen potential (Oxygen potentiaI), which is the basic condition for producing slag with good inclusion trapping ability and degassing capacity, that is, FeO, In order to keep the MnO component low, it is put on top of the slag introduced into the small aluminum slug.

After blowing the 100-500ℓ / mim argon gas per ton of molten steel using a deodorizing lance, and performing the steel bubble blowing, and using the degassing equipment, injecting the argon gas of 250-400ℓ / hr per ton of molten steel to less than 2torr in high vacuum for dehydrogenation. -15 minutes treatment.

In this case, in order to protect the deposition pipe of the degassing facility, the softwood and water having the components shown in Table 1 are mixed inside and outside the deposition pipe, and the material is sprayed 10-20 minutes before degassing using air. do.

TABLE 1

However, this method is sprayed 10-20 minutes before the degassing treatment, which increases the initial hydrogen, the control limit of aluminum or sulfide inclusions, and the limitation of degassing. There is a problem that is impossible to use.

The present inventors conducted research and experiments to solve the above problems of the conventional methods, and based on the results of the present invention, the present invention primarily increases the agitation time and inclusion separation injury time, and dewatering By blowing zein calcium-silicon (Ca-Si) into molten steel and stirring the steel during blowing, it promotes deflow reaction, produces low melting point inclusions, facilitates separation injury, and also spheroidizes the residual inclusions and increases the initial increase of initial hydrogen. The purpose of the present invention is to provide a method for manufacturing a highly clean low hydrogen thick plate material by reducing hydrogen by securing a drying time after the spray is carried out in order to prevent.

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

The present invention deoxidizes molten steel with deoxidizer containing aluminum during tapping from converter to ladle, and adds lime to the slag, and then adds aluminum to the upper part of converter slag introduced into the ladle after tapping to obtain slag with excellent dewatering ability and absorption of inclusions. In the method of preparing a thick plate material by bubbling the molten steel and slag in the ladle in a bubbling stand, and then degassing in a degassing facility including a vacuum bath and a deposition tank, 0.7-1.0 kg / tonne of calcium silicon-based desorbent is blown by using; In addition, the spray material mixed with aluminum or refractory water is sprayed on the deposition pipe of the degassing facility at least 30 minutes before the degassing treatment, and degassed for 10-15 minutes with high vacuum of 2torr or less. It relates to a manufacturing method.

Slag which is excellent in the degassing ability and the inclusion absorbing ability manufactured at the time of manufacture of thick plate material is weight%, CaO: 45-55%, AI ₂ O ₃ ; 25-35%, and SiO ₂ ; Slag containing 8-10% and having a basicity (CaO / SiO 2) of 5.0-8.0. In the present invention, it is preferable to bubble strongly at the time of bubbling at the bubbling stand.

Calcium-silicone desorbent added in the present invention is blown by the upper lance using an inert gas such as argon gas, promotes the dehydration reaction by the steel stirring and the separation separation inclusions and the inclusions difficult to separate the separation reaction with Ca To act to shape the inclusions.

At this time, the calcium-silicone dehydrating agent introduced in the present invention may use a conventional calcium-silicone dehydrating agent, for example, by weight% Ca; 30% or more, Si; 55-65%, C; 1.4% or less, P; 0.05% or less and calcium-silicone desorbents composed of other unavoidable impurities.

However, when the amount of calcium-silicone desorbent is less than 0.7Kg per ton, the addition effect is insufficient due to the reduction of the reaction chance of calcium and silicon injected into the molten steel and the inclusions in the molten steel. Because the molten steel is contaminated by the reverse flow of molten steel and slag and the temperature drops, it is inevitable to shorten the degassing treatment time, and the lack of continuous casting connection time is not performed smoothly. It is desirable to limit to 0.7-1.0 Kg.

In addition, the particle size of the calcium-silicon releasing agent is preferably limited to 40 mesh or less.

On the other hand, in the present invention, in order to protect the immersion tube, a spray material mixed with alumina refractory material for protecting the immersion tube is applied to the immersion tube, followed by degassing treatment. The spraying material is preferably applied for 30 minutes or more before degassing treatment. It should be done 30 minutes to 1 hour before, since it is possible to prevent the increase of hydrogen by ensuring sufficient drying time.

At this time, the alumina refractory for protecting the dip tube used in the present invention may use a conventional AI ₂ O ₃ -SiO ₂ refractory, for example, AI ₂ O ₃ ; Preference is given to alumina refractory comprising at least 80% by weight and composed of up to 18% by weight of SiO ₂ and other unavoidable impurities.

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

EXAMPLE

When tapping molten steel at 1710 ° C from a converter with a capacity of 300 tons, it deoxidizes to 750Kg of 95% by weight grade aluminum and taps into the ladle while adding 2.4 tons of quicklime. Deoxidation of FeO and MnO, blowing argon gas at a flow rate of 3.5 Nm ³ / min using a deodorizing lance, and performing 5-5 minutes of strong bubbling, using the decanting agent of Table 2 per molten steel in the molten steel 0.7 kg was blown.

As a comparative example, also in the case where there was no injection of calcium silicon according to the conventional method, deoxidation, quicklime injection, and strong bubbling using argon gas were performed at the time of tapping and after tapping.

Next, after degassing for 10-15 minutes in a high vacuum of 2torr or less in a degassing facility, a thick plate material was produced.

At this time, in order to prevent sedimentation pipe connection, partial dropout and cracking by erosion of the degassing facility deposition pipe, the refractory material of Table 1 is mixed with water and sprayed on the deposition pipe in the conventional method. In the present invention method, however, molten steel having undergone the above step 1 was carried out 30 minutes before arriving at the degassing facility. The total oxygen amount according to the calcium-silicone desorbent blowing amount using the upper lance and the total oxygen amount for the case where no desorbent was blown (conventional method) were measured, and the results are shown in FIG.

In addition, the hydrogen content change according to the degassing time after the deposition pipe spray before degassing was investigated, and the results are shown in FIG. 2.

In addition, the defect rate by the defect was investigated by the ultrasonic flaw detection method, and the result is shown in FIG.

In addition, the sulfur content of the segregated portion and the Charpy impact value at −45 ° C. were investigated, and the results are shown in FIG. 4 for the sulfur content of the segregated portion and FIG. 5 for the Charpy impact value.

TABLE 2

TABLE 3

As shown in FIG. 1, it can be seen that the method of the present invention is superior to the conventional method when compared with the average value of the total oxygen amount represented by the amount of strong oxide inclusions, which is a dimension of cleanliness.

In addition, as shown in FIG. 2, the present invention shows an excellent hydrogen content reduction effect compared to the conventional method, which is lower in initial hydrogen content than the conventional method when dried for 30 minutes or more, and degassed under high vacuum for 10-15 minutes. This is because the hydrogen concentration decreases later.

In addition, as shown in FIG. 3 and FIG. 4, the stretch inclusion of MnS is spheroidized by the calcium-silicone type | system | group degassing agent injection of this invention method, and as shown also in segregation degree, it is seen that the sulfur concentration of a segregation part becomes small. It can be clearly seen that the inventive method significantly reduces the defective rate compared with the conventional method.

In addition, as shown in FIG. 5, it can be seen that the method of the present invention is superior to the conventional method even in the impact value.

That is, in the present invention method, the calcium silica can be injected and the drying time after the internal and external spraying of the deposition and protective refractory materials is secured, and the treatment rate under high vacuum can greatly reduce the defect rate caused by the ultrasonic inspection, and even in the amount of oxygen By showing a value and greatly improving mechanical properties such as impact value, toughness, and bendability, it can be seen that the present invention method is superior to the conventional method.

As described above, according to the present invention, the segregation degree reduction degree MnS and the alumina-based inclusions spheroidization and the total amount of oxygen by using calcium silicon easily obtained in the steelmaking process and effectively using materials that delay the refractory erosion of the degassing plant There is an effect that can produce a low hydrogen high clean thick plate material according to the hydrogen reduction.

Claims (1)

Deoxidizer containing aluminum during tapping from converter to ladle is used to deoxidize molten steel and add quicklime, and after finishing tapping, aluminum is added to the top of the converter slag introduced into the ladle to prepare slag with excellent dewatering ability and absorption of inclusions. A method of manufacturing a thick plate material by bubbling molten steel and slag in a ladle in a bubbling stand, followed by degassing in a degassing facility including a vacuum tank and a settling tank. 0.7-1.0 Kg per ton of molten calcium-silicone desorbent of the blow-in; And 30 minutes or more before degassing, the spray material mixed with alumina refractory material with water is sprayed on the deposition pipe of the degassing facility and calgas treatment for 10-15 minutes with high vacuum of 2torr or less. Method for producing a clean thick plate material.