JPS591620A - Refining agent having high desulfurizing power causing slight melt fracture on refractory - Google Patents

Abstract

PURPOSE:To increase the desulfurizing power of the resulting refining agent, to reduce the melt fracture on refractories, and to make the agent inexpensive by providng a specified composition contg. CaO, Al2O3, CaF2, an alkali metallic oxide or carbonate, and MgO. CONSTITUTION:This refining agent is obtd. by combinedly adding 5-20wt% alkali metallic oxide or carbonate and 3-10wt% MgO to a mixture consisting of, by weight, 30-70% CaO, 10-40% Al2O3 and 5-30% CaF2. The refining agent is suitable for use in the desulfurization of molten steel, especially molten stainless steel which is difficult to desulfurize.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refining agent for removing sulfur from molten steel, particularly stainless molten steel, which is difficult to remove sulfur from.

In recent years, the quality required for steel materials has become increasingly strict and diversified, and there is a desire for steel manufacturing technology that can produce steel with higher purity at a lower cost. For this reason, a variety of so-called ladle refining techniques and various refining agents have been developed and utilized as auxiliary means for conventional steel manufacturing methods, leading to the creation of a new field of metallurgy.

The need for quality 11' is no exception for stainless steel, which is an Or-containing steel.Recently, in order to improve the induction resistance of 190R steel, which is a molding material for automobiles, various studies have been conducted to reduce the product S of this steel type as much as possible. ing.

This is the result of a comprehensive study on six different S-removal refining agents to address this problem.

Ca O+ A A203 + Oa F 2 + alkali metal oxide or carbonate, a refining agent mixed with M10'ii appropriate composition has excellent S removal ability, is inexpensive, and has little effect on Vctlj refractory erosion. It was confirmed that it is extremely effective.

That is, 1 gist of the present invention 1jOa030
~70% by weight, AtzOa 10-40 times maximum.

5-20% by weight of alkali metal oxide or carbonate based on a mixture consisting of 0aF25-30% by weight.

The object of the present invention is to provide a refining agent with a high ability to remove S, which has a low erosion effect on inexpensive refractories containing 3 to 10% MiOk composite.

Conventionally, [AOD] was used as a S removal technology for molten stainless steel.

1. Using a secondary refining furnace such as F, 0a00 as a refining agent.
aF2 series or OaO-S i02 0aF2 series.

A common method was to add Ca OA A203 0 a F2-based flux and perform reduction refining. However, Oa O-Ca ``'2 system and OaO-S
The i02-CaP2-based flux had drawbacks such as weak S removal ability and strong erosion effect on refractories. Further, although CaO-A j203 CE a F2-based flux has considerably improved S removal ability, it has a drawback in that it has a large erosion effect on refractories.

In view of the situation described above, the inventors have developed fiOao-A.
A203 0 a F2 series flux as pace.

Refining agent V with excellent S removal ability and low refractory erosion effect
Various studies were conducted regarding C. As a result, the weight percentage is 0a
030～. 70%, A4203 10-40%, Ca
It is clear that a flux containing 5-20% total alkali metal oxide or carbonate and 3-10% MpO is optimal for a mixture of 25-30% P.

KCaOn is the main component for S removal, and if it is less than 30%, a sufficient S removal effect cannot be obtained, and if it is more than 70%, the melting point of the flux increases and the S removal ability is drastically reduced. In addition, it forms CaO and calcium aluminate on At203, which plays an auxiliary role in promoting desulfurization by Ca0K, and when the concentration is below 10, the formation of calcium and aluminate is insufficient, so the desulfurization ability deteriorates. However, if it exceeds 40 qb, calcium and aluminate must be converted to OaO to remove S, which is not preferable. S
It is said that it plays a role in promoting the movement of OaO to the OaO surface.

On the other hand, *lowering the melting point of Oa F2 i11 flux
It is a component that promotes deS removal, and if it is less than 5%, the effect of lowering the melting point is insufficient, so it is preferable. Moreover, if it exceeds 30%, the refractory material will be significantly damaged and it will be disadvantageous in terms of cost.

The reason why the alkali metal oxide or carbonate is the largest by weight is 5 to 20 in the above basic composition.

This is to improve the ability to remove S. U N a 20 T N a 2 C as an oxide or carbonate of an alkali metal
Typical examples include O3+ K20+, 2Co, etc.
These 1 have high S ability by themselves, and when combined with 5 or more elements, the improvement in S ability is remarkable.

However, if it is 20% or more, it is preferable because the effect of erosion of the refractory becomes large. Therefore, it is preferred that the alkali metal oxide or carbonate has a maximum weight ratio of 5 to 20%.

Also, MiO'? f The reason why the weight is 3 to 10% is to protect the refractory. When MJlo is less than 3%, the effect of protecting the refractory is insufficient, and when it is more than 10%, the melting point of the flux increases, which is preferable. Therefore, the appropriate addition ratio of Mv0 is at most 3 to 10% by weight relative to the flux having the above basic composition.

Next, we will discuss the particle size of flux. The particle size of the flux is not particularly limited, but from the viewpoint of increasing the efficiency of one reaction, the finer the particle size, the better.

However, in the so-called flux top-up method in which all the flux is added from the top of the reaction vessel, if the particle size becomes fine, losses such as suction like dust collection occur, which is undesirable.

According to the experience of the present inventors, the appropriate flux particle size for the flux overlay method is 0.5 to 10 ma. 0 here
．． If it is less than 51, losses due to scattering etc. will occur, and if it is more than 10, it will be difficult to melt and the reaction efficiency will decrease. It is also possible to use a fully immersed flux lance to directly inject the flux into the molten stainless steel along with an inert gas such as A. In this case, the optimal flux particle size is 0.1 to 0.5. ．．
If it is over 5ma, nozzle clogging will occur due to slacks.
In addition, if it is less than one sail, it becomes extremely fine powder, making handling such as transportation difficult.

Among the flux components, quicklime and fluorite may be used as the OaO and OaFz sources, respectively.

As an At203 source, it is possible to effectively utilize alumina dross, which is a by-product of so-called A4 smelting, and as an MIO source, dolomite, which is a mixture of OaO and MIO, may be used.

Note that it is also possible to use the flux of the present invention by sintering it in advance, and in this case, the melting of the flux is sufficiently promoted and the reaction efficiency is improved.

Of course, the present invention is also effective for general carbon steels, etc., which have a strong need for flux reduction and low S.

Next, the effects of the high S removal refining agent according to the present invention will be specifically described.

The hot metal in the 120 ton converter is subjected to dephosphorization refining in advance, and after the slag is discharged, Fe-C! Crude molten stainless steel obtained by adding RF, melting and removing C, and then finishing and adjusting the C1 component by RH refining.
The composition and temperature are shown in Table 1), and all types of stainless steel were added to perform S-free refining. The processing conditions are as follows: (1) Processing amount Ni stainless steel crude molten steel 100-115
2) De-S method: Using R and II, the entire melt-resistant stainless steel is refluxed and slack is added into the vacuum chamber (3) Processing time = 30 to 40 minutes (4) Stainless steel particle size: 1 to 5 (5) Flux Addition amount: 13-16 Kg/1
．． s flux is B: 0aO-OaF2 type plush flux 00aO
-8i02-0aFz system flux D: 0aO-A
Four types of t203-Oa P2-based fluxes were subjected to S-removal refining using three charges each.

Table ff1 Composition and temperature of crude molten stainless steel As a result, the S removal effect shown in FIG. 1 and the state of refractory erosion shown in FIG. 2 were clarified. That is, FIG. 1 shows a comparison of the average S removal rates of three charges of S removal treatment for each flux. As with 7lux D, the highest S removal rate was obtained with the flux.

In addition, Figure 2 shows the state of refractory erosion in the 3-charge S removal process for each flux, and the MVO eluted into the slag.
These are the results of a comparison using MrO (the main component of the refractory in the R.H tank) as a measure. The amount of MtO elution is Flux A 0.07 Kg/t. s h stainless steel C
0-1 5 K9/t. s 1 flux B O.
1 8 Kda/+. s.

Flux 0 0.3 0 Kg/t. It increases in the order of s.

It can be seen that the flux according to the invention is extremely advantageous from the point of view of protecting refractories.

Regarding eluted MIJO, calculate the amount of slag produced from the amount of CaO in the supplied flux and the CaO analysis value (%) of the produced slag, and calculate the amount of slag produced and the M of the produced slag.
The amount of MjlO eluted was calculated from the IO analysis value.

As is clear from the above explanation, the flux according to the present invention has excellent S removal ability and also has a large effect of protecting refractories, and can be said to be an extremely practical refining agent. Therefore, by utilizing and using the high S-removal ability refining agent of the present invention, S can be reduced to 0 before treatment even in steel types where S removal is relatively slow, such as stainless steel.
．． 0 0 If it is about 5%, it will be stable after treatment.
O. It is possible to reduce the S content to 0.02% or less, which not only satisfies material needs, but also allows a S-free refining process to be carried out at an extremely low cost, which is beneficial to the steel industry.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the average desulfurization rate depending on the type of flux.
FIG. 2 is a comparative diagram of the MIO elution pattern depending on the type of flux. Agent Patent attorney Masaaki Aki Sawa Mitsunobu 2 people fr1 Figure 9 5-fold ('/,) 'iZ diagram Hri O denshi quantity (k@A-5)

Claims (1)

[Claims] (It 0a030-70% by weight, AtzOa
5 to 40% by weight of alkali metal oxide or carbonate to a mixture consisting of 25 to 30% by weight of 0aF.
1. A refining agent with high S-removal ability that has little erosion effect on refractories, characterized in that it has a maximum Mlo content of 20% by weight and 3 to 10% by weight.