JPH0130890B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a steel refining agent for desulfurization, deoxidation, dephosphorization, etc. in steel refining. This refining agent has particularly excellent digestion resistance. In steel refining, molten steel is treated by adding a scouring agent (flux) for desulfurization, deoxidation, etc., but in recent years, the injection treatment method, in which powder or granular flux is injected into molten steel with high-pressure gas, has been used. is becoming popular. Flux treatment is also performed in other electroslag scouring methods and continuous casting. Scouring agents used in these treatments include
Mixed systems such as Ca-Si alloys, CaC ₂ , CaO, CaF ₂ , and Al ₂ O ₃ are known. Ca-Si alloys are inefficient because Ca easily evaporates at the molten steel temperature.
This not only leads to an increase in Si, but also has the disadvantage that Ca reduces Al ₂ O ₃ in the furnace refractories to produce Al, resulting in an increase in Al in the molten steel. CaC ₂ has been known for a long time as a desulfurization agent, but it has the disadvantage of increasing the carbon content of molten steel, so it is disliked especially when steel with a low carbon content is intended. Powder mixtures of CaO, CaF ₂ , and Al ₂ O ₃ or mixtures and sintered granules have also been proposed, but these take a long time to melt when injected into molten steel, so they are particularly difficult to use. When using the blowing method, the scouring agent melts in the molten steel and floats to the surface before performing desulfurization or other actions, resulting in insufficient effects. As a method to solve this problem, it has been proposed to melt and cast these scouring agents, and then crush this into powder or granules. However, systems containing CaO are generally digestible, and if they are in granular form, they will turn into powder as they react with atmospheric moisture to produce hydroxide. Digested steel is not only difficult to handle, but also contains hydrogen, so adding it to molten steel will significantly increase the hydrogen content in the steel, which is undesirable. This digestibility is
Sintered products and electromagnetic pulverized products have been improved over CaO powder mixtures, but they are still not sufficient. Although electrolytically pulverized products have considerably improved digestibility, pulverization requires a large amount of mechanical energy, and the yield of particles of uniform particle size is extremely low. The present invention has a large scouring agent effect and is highly resistant to digestion.
It provides a CaO quality steel refining agent. That is, the present invention is a digestible calcareous steel refining agent which has a composition consisting essentially of CaO and the remainder is unavoidable impurities, and is in the form of melt-solidified, uncrushed granules. CaO is generally made from limestone, so it is usually
Contains impurities such as SiO ₂ , Al ₂ O ₃ , Fe ₂ O ₃ and MgO. Since the scouring agent of the present invention is mainly made by melting and solidifying this raw material, it contains such unavoidable impurities. This impurity is usually less than 5%. Although the present invention is thus a scouring agent consisting essentially of CaO, it may be used in combination with other components. The scouring agent of the present invention has a spherical or nearly spherical granular shape, has a relatively smooth surface, and is composed of microcrystals both on the surface and inside. Another feature is that the surface does not have a fractured surface. These points are fundamentally different from those obtained by crushing a cast body into granules. The crushed product has a non-smooth surface with many corners, and the surface is a crushed surface. Further, since the cast body cannot be rapidly cooled to the inside thereof, the size of the crystals in the crushed product is larger than that of the product of the present invention. According to research conducted by the present inventors, it has been found that these granular products having a crushed surface do not have sufficient digestion resistance. The scouring agent of the present invention improves these drawbacks by rapidly cooling the molten droplets with the above-mentioned composition and turning them into the final product as is.Since the scouring agent is not crushed, there is no crushing surface, and the cooling of the molten droplets The solidified granules are microcrystalline to the inside because they are rapidly cooled to the inside. The size of most of these granules is 2 mm or less. The scouring agent of the present invention can be used for injection in steel smelting for the purpose of desulfurization, deoxidation, dephosphorization, etc., electroslag scouring, continuous casting, etc. Especially for injection, it has a nearly spherical granular shape, so it can be used for blowing. It is convenient for In addition, it is highly resistant to digestion, so it is easy to store and handle. Next, the manufacturing method will be explained. Raw materials such as limestone and quicklime are melted in a tilting electric furnace. After melting, the molten metal is allowed to fall by tilting, and a gas such as compressed air is blown from a nozzle into the falling flow to blow off the molten metal, turning the molten metal into droplets and rapidly solidifying them. The size of the particles varies somewhat depending on the blowing conditions, but most are 2 mm or less. Another possible manufacturing method is to drop the molten metal onto a rotating plate and use centrifugal force to scatter the molten metal into particles from around the plate, thereby rapidly solidifying the molten metal. This method yields dense solid spheres in most cases. Example Limestone was melted in an arc furnace and blown away with compressed air to obtain granules having the composition shown in Table 1, No. 1. The blowing conditions were molten metal falling amount (Kg/min)/air volume (Kg/min) = 7, and nozzle air pressure 5Kg/cm ² .
The obtained granules had the following particle size distribution. 1000 μ or less 1000 to 2380 μ 2380 μ or more 65% (weight) 28% 7% For comparison, CaO pulverized product No. 2 and the same melt-casted pulverized product No. 3 were prepared. No. 2 and No. 3 were pulverized and adjusted to have almost the same particle size distribution as above.

【table】
(Numbers are weight%)
(1) Digestion resistance test 10g of samples No. 1, 2, and 3 were placed in a dish, exposed to air (temperature 30°C, humidity 90%), and changes in weight increase due to water absorption over time were observed. The result is the first
As shown in the figure. In FIG. 1, the horizontal axis is the number of days that have passed, and the vertical axis is the weight increase rate (weight %). (2) Molten steel scouring test CaF ₂ ,
Mix _Al2O3 , _MgO , CaO65%, _CaF216
%, _{Al2O3 15} %, MgO2%, SiO2 ₁ %, _{Fe2O3 1}
A scouring agent with a composition of % was prepared. This scouring agent was blown into a 30 kg steel bath that had been high-frequency melted in a magnesia crucible through an 8 mm diameter alumina tube together with Ar gas at 4/min.
The steel bath temperature is 1600℃, and the scouring agent blowing rate is 15g/
min, blowing time 15 minutes. Table 2 shows the analysis results of impurities before blowing and after blowing.

[Table] As can be seen from Table 2, since scouring agents No. 2 and 3 have been digested, the H content in the steel using them is high.

[Brief explanation of drawings]

FIG. 1 is a graph showing the elapsed days and weight increase rate of the scouring agent.

Claims (1)

[Claims] 1. A digestible calcareous steel refining agent which is composed of substantially CaO and the remainder is unavoidable impurities, and is a melt-solidified, non-fragmented granular material.