JPH01129925A - Method for adding calcium to molten steel - Google Patents

Abstract

PURPOSE:To prevent the emission of smoke at the time of addition of a granular or lump Ca additive and to increase the addition yield of Ca by coating the surface of the additive with refractory and/or iron powder. CONSTITUTION:A granular or lump Ca alloy and/or Ca-contg. metal additive contg. 3-35% Ca and surface-coated with refractory and/or iron powder is added to molten steel in an RH degassing tank. MgO, Al2O3, SiO2, fluorite or other metal oxide is suitable for use as the refractory and two or more kinds of such metal oxides may be used in combination. By the surface coating, the reaction of the Ca additive is retarded, the emission of white smoke at the time of addition can be very simply prevented and an yield increasing effect is produced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for adding calcium to molten steel with good yield.

(Prior Art) In general, deoxidation and desulfurization are performed as essential scouring steps in the steel scouring process. Among them, deoxidizing has recently been relatively easily performed using various known deoxidizing agents, and vacuum degassing technology and D
With the development of various scouring methods such as the H method, RH method, vOD method, and AOD method, deoxidation treatment can now be performed relatively easily.

On the other hand, with regard to desulfurization, the mainstream is desulfurization using slag, especially desulfurization by a chemical reaction that creates carbide slag, and similar methods include those using CaO, those using CaO and CaF2, Nal COs, etc. There is a way. However, these slag-making methods require a certain amount of reaction time, and the carbon concentration may increase or the sulfur content may be extremely low, such as when the S content is o or oo.
If it is less than s%, there is a drawback that the efficiency is poor and it takes too much time.

In order to correct these defects, a method of directly adding desulfurization elements to molten steel is disclosed, for example, in JP-A-52-139623, JP-A-53-12411, or JP-B-Sho 57-15170. Various proposals have been made. In most of these methods, desulfurization elements are added to molten steel that has been sufficiently deoxidized in order to increase the addition efficiency. The reason is that strong desulfurization elements generally have a strong affinity for oxygen, so in order to increase desulfurization efficiency, it is necessary to
That is, this is because it needs to be performed immediately before casting. Furthermore, if desulfurization is performed immediately before casting, there will not be enough time for the generated non-metallic inclusions to float away, so it is important that the generated inclusions are not in a harmful form. Ca, which does not easily form metal inclusions, has been commonly used. In addition, Ca has been widely used in recent years to control the shape of nonmetallic inclusions.

Conventionally, methods for efficiently adding calcium to steel include: ■ Injecting calcium silicide or nickel calcium, as represented by calcium silicide, into the flow during tapping; ■ JP-A-52- As shown in Publication No. 139623, a method of wrapping metallic calcium in a long and thin mild steel plate to form an electric wire shape and continuously pushing it into steel, ■ Metallic calcium or Ca
A method in which alloys, iron-lucium briquettes, etc. are added to steel using a pouring plunger or other methods; ■ An injection method in which Ca or Ca alloy powder is injected into molten steel using an inert gas; Methods such as inserting a solid bar into molten steel in a ladle, and ■continuously adding granular products using a tongue push are known.

(Problems to be Solved by the Invention) However, problems common to these methods are that calcium is a very active metal, so it is difficult to control the white smoke generated during addition and the violent reaction. There are problems with the work process, such as the fact that there is a large amount of oxidation, and that a very complicated addition operation is required. For example, currently the most commonly used ■
This method causes an increase in the concentration of nitrogen introduced into the carrier gas and a decrease in temperature, and the cost and time required for the inert carrier gas and lance pipe to be blown into the carrier gas are major problems.

In addition, we focused on the fact that high-grade steel, which generally requires Cafi treatment, is degassed in an RH degassing device, and after the degassing treatment, the degree of vacuum in the RH degassing tank is slightly reduced to remove Ca additives. It is possible to add 2
Molten steel will not reflux unless the pressure is reduced to 0.00 Torr or less, and Ca additive has extremely high activity and boils and evaporates at 1483°C, so the moment it comes into contact with molten steel, Ca burns and evaporates. However, since the evaporated Ca gas was dissipated in the suction hood, the yield was extremely low and it was extremely impractical.

Currently, in steel refining, controlling the shape of nonmetallic inclusions by adding Ca is an essential condition for producing high-grade steel, and the need for this is increasing to prevent nozzle clogging. At present, there is no suitable and satisfactory method among the various methods listed above.

(Means for Solving the Problems) The present invention was made for the purpose of developing an extremely simple and non-polluting addition method that does not generate smoke at all.
As a means to solve the above problems, the surface is coated with a refractory material and/or iron powder, and the calcium content is 3 to 35%.
The present invention provides a method for adding calcium to molten steel, which comprises adding a granular or lumpy calcium alloy and/or a calcium-containing metal additive to molten steel in an RH degassing tank.

That is, in the present invention, although the reflux of molten steel is performed sequentially in the RH degassing tank, if Ca is substantially added when the molten steel returns to the ladle according to this flow, evaporation will occur. Focusing on the fact that calcium evaporation does not occur because there is no decompression time, the surfaces of each particle or lump of Ca alloy and Ca additive are coated with refractory or iron powder that is not harmful to molten steel, or The reaction is delayed by coating with alternating layers of powder and refractory, or a mixture of both.

As the calcium alloy, Fe-Ca-3i alloy,
Fe-Ca-Si-RE gold alloy Fe-Ca-Ni-3i
Any alloy such as Ni-Ca alloy, Ni-Fe-Ca alloy, and Cu-Ca alloy can be used, and these alloys can be used alone or in combination of two or more, and the particle size can also be set arbitrarily. You can choose.

In addition, a representative example of the calcium-containing metal additive is an Fe-Ca briquette obtained by compression molding a mixture consisting of 3 to 35% metallic calcium and the remainder substantially iron powder, but is not limited thereto. It is not something that will be done.

The surface of the particles or lumps of the granular or lumpy calcium alloy or calcium-containing metal additive is coated with a refractory material or fine iron powder, but as a refractory material,
Magnesia, alumina, silica, fluorite and other metal oxides are preferred. These metal oxides may be used alone or in combination of two or more, or may be used in combination with iron so that the metal oxide and iron are alternately coated.

In addition, the Ca additive cut out from the addition hopper by the coating is sucked up from the ladle and comes into contact with the refluxing molten steel, but unlike conventional Ca additives, there is no instantaneous reaction and it takes several seconds depending on the thickness of the coating. The thickness of the coating is adjusted so that the reaction occurs after several tens of seconds, that is, when the molten steel during reflux incorporates these additives and returns to the ladle, the reaction occurs in the ladle that is not under reduced pressure. It is suitable for adjustment.

(Function) According to the method of the present invention, the molten steel is degassed by being refluxed into the depressurized RH degassing tank by inserting a conduit above the molten steel in the ladle, and the alloy addition hopper provided at the upper part From, F
e-Ti, Fo-Cr, Fe-Mo.

R to cut out and add alloy additive elements such as Fa-Si
Immediately after the deoxidation and degassing treatment, Ca addition treatment is carried out using a H degassing tank at a place where the concentration of oxygen is low.Moreover, the calcium alloy or calcium-containing metal additive is made into granules or lumps, and the surface is Refractory materials and/or
Alternatively, since it is coated with iron powder, the reaction of the Ca alloy and/or Ca additive is delayed, resulting in an effect of improving the yield.

The Ca reaction can be delayed by reducing the Ca content, but if the Ca concentration is 3% or less, the amount added becomes too large, resulting in an increase in the absolute amount, a decrease in temperature, and a reduction in processing time. Since this is undesirable, the lower limit of the calcium content in calcium alloys and calcium-containing metal additives is set at 3% or more.

Furthermore, if the calcium content exceeds 35%, the yield will be poor no matter how many reaction suppression methods are used, so the upper limit was set at 35%.

That is, in the method of the present invention, since the surface of the Ca additive added in the RH degassing treatment tank under reduced pressure is coated, the Ca additive is not contained in the RH degassing layer but is substantially refluxed. Since Ca reacts in a pot, it was previously extremely difficult to remove Ca.
It can significantly improve the addition yield and has extremely high utility value in industrial mass production.

Next, examples will be described.

Example (1) ■ Cal 0%, Si 45% remaining F consisting essentially of iron
Using the e-3i-Ca alloy, general steel was treated in a 250 ton RH degassing tank as follows. That is, after degassing by reducing the pressure from normal pressure to 0.3 to 4 Torr and returning it to 120 Torr, the Fe-Si-Ca
After continuously adding 500 kg of the alloy, the pressure was returned to normal pressure by about 1 reflux.

(2) The surface of Fe-Si-Ca alloy particles having exactly the same composition as above was coated with a mixed refractory of magnesia, alumina, silica, and fluorite to a thickness of 1 to 3 m/m. A net weight of 500 kg of the alloy was added under the same conditions as in (2).

The calcium yield of each of the above-mentioned general steels was investigated and was as shown in Table 1.

Table 1 Example (2) ■ Metallic Ca powder 1O% Using high-pressure granulated iron-Ca briquettes, the remainder of which is essentially iron powder, general steel was treated in a 50-ton RH degassing tank as follows. did. Initially, the pressure was reduced from normal pressure to 0.3 to 4 Torr for degassing treatment, and then 500 kg of the above-mentioned iron-Ca briquettes were continuously added while increasing the pressure in the tank to 130 Torr. The pressure was returned to normal pressure at around reflux.

■ The surface of an iron-Ca briquette with the same composition as above was coated with the same magnesia + alumina + silica + fluorite refractory used in Example (1) to a thickness of 1 to 2 m/m. , and then coat the top with fine iron powder to a thickness of about 1m/
Net weight of double-coated iron-Ca briquettes of about 5 m
00 kg was added under the same conditions as ().

When the yield of calcium in the steel thus obtained was investigated, the results shown in Table 2 were obtained.

Table 2 (Effects of the Invention) As is clear from the above explanation, according to the present invention, ■
Immediately after deoxidation and degassing treatment has been performed in the RH degassing tank, Ca treatment is possible at a place where the concentration of oxygen is low. No equipment or equipment is required, and Ca treatment can be carried out smoothly in the normal work flow; ■ Reaction time is not required, eliminating time loss; ■ Temperature drop can be minimized due to ■■ reasons. ■The RH degassing tank equipment usually has a flue gas dust collector, so this can be used automatically, so there is no need for a special dust collector for intense Ca processing gas. Calcium addition can be achieved under reduced pressure and at a high yield. In other words, it is possible to add calcium, which easily evaporates even at molten steel temperature, in a near-vacuum/vacuum pressure tank, and to add calcium at a high yield. It has excellent effects such as being able to satisfy the extremely contradictory demands of obtaining yield.

Patent applicant: Osaka Special Alloy Co., Ltd.

Claims (6)

[Claims] (1) Granular or lumpy calcium alloys and/or calcium-containing metal additives whose surfaces are coated with refractory materials and/or iron powder and which contain 3 to 35% calcium are added to molten steel in the RH degassing tank. A method for adding calcium to molten steel. (2) The calcium alloy is a Fe-Ca-Si alloy, F
e-Ca-Si-RE alloy, Fe-Ca-Ni-Si alloy, Ni-Ca alloy, Ni-Fe-Ca alloy, and C
2. The method according to claim 1, wherein the material is at least one selected from the group consisting of u-Ca alloys. (3) The calcium-containing metal additive is an Fe-Ca briquette obtained by compression molding a mixture consisting of 3 to 35% metallic calcium and the remainder substantially iron powder. The method described in section. (4) The method according to any one of claims 1 to 3, wherein the surface of the granular or lumpy calcium alloy or calcium-containing metal additive is coated with fine iron powder. (5) Any one of claims 1 to 3, characterized in that the surface of the granular or lumpy calcium alloy or calcium-containing metal additive is alternately coated with a refractory material and iron. The method described in paragraph 1. (6) The method according to any one of claims 1 to 4 and 5, wherein the refractory material is a metal oxide.