JPS61195934A - Flux for electro-slag remelting - Google Patents

Abstract

PURPOSE:To attain a high yield of S in the electro-slag remelting of an alloy contg. S by specifying the amount of CaO, Al2O3 and CaS as the essential components of a flux. CONSTITUTION:A flux consisting essential of 20-55wt% CaO, 35-60wt% Al2O3 and 2-30wt% CaS is used in the electro-slag remelting of an alloy contg. S such as a free-cutting steel. The flux may further contain <=10wt% MgO substituted for part of the CaO. By the composition of the flux, a high yield of S can be attained in the electro-slag remelting of the alloy contg. S, and the quality of the free-cutting steel can be improved as desired.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a flux for remelting electroslag that can achieve a high yield of sulfur in alloys containing sulfur, such as free-cutting steel. .

[Conventional technology] Sulfur concentration 0.0! For steels or alloys of less than 100%, electroslag remelting (hereinafter sometimes referred to as ESR) may be performed to improve the quality of the material, including desulfurization, etc. In such cases, In ESR, CaF2- A 1203 series, CaF2- CaO-
It is common to use ESR fluxes of A1zO:+ system and Ca0-Al2O2 system.

However, with the progress of mechanization and automation in factories in recent years, there has been an increasing demand for longer tool life, improved surface finish accuracy, and improved chip disposal in cutting operations. Free-cutting steel with a sulfur concentration of 0.01% by weight or more is becoming increasingly important.

However, the above-mentioned C
AF2-A 120s type flux and the like are widely used, and it is known that the desulfurization effect of the flux is exerted and the sulfur concentration decreases. That is, E
It cannot be said that the intended purpose of SH has always been satisfactorily achieved, and there is a need for a new flux for ESR that can replace GaF2-^203-based flux and the like. In addition, so far, JP-A-49-82311 and 57-
No. 85941 and the like have been proposed, and electroslag remelting fluxes for sulfur-containing steel have been disclosed, but all of these are considered to be beyond the basic composition of the fluxes described above.

[Problem to be Solved by the Invention 1] The present invention has been made in consideration of the above circumstances, and is a method for achieving a high yield of sulfur in alloys containing sulfur, such as free-cutting steel. The aim is to provide a flux for ESR that can be used.

[Means for Solving the Problems] The flux for ESR according to the present invention is used when electroslag remelting the alloy containing I & yellow, and (1) Cab: 20 to 55% by weight (hereinafter simply%
), (2) A1203: 35-60%,
(3) CaS: The gist lies in having a composition in which each content is 2 to 30%.

Then, the condition (3) above is changed to (3a) Ca S Os
:2 to 30% in CaS conversion! ! Replaced ESR flux (3b) with Ca, Mg, and AL at the same time.

Oxidizable metals such as St or alloys thereof; ESR 7lux containing the necessary amount to reduce CaSO4 to CaS can also be used as ESR flax 7 with a composition that satisfies the above (1) to (3). Achieve the same purpose as Kusu.

C action] The woody characteristics of the present invention are CaO-A1203-C, which is a flux for ESR used in electroslag remelting of sulfur-containing alloys such as free-cutting steel.
Select aS-based fluxes and use these CJLO, A120
3. Since each content rate of CaS has been empirically defined, this point will be mainly explained below.

(Todoroki) Regarding the reason for using CaO-Al2O2--Ca'J-based flux, especially CaS: Ordinary fluxes such as ESR whose main component is CaFz
When a commercial flux is used, the evaporative desulfurization reaction shown in the following formula proceeds, and the sulfur component in the flux is oxidized by atmospheric oxygen.

(32-) +3/202→S02 + (02...
-(1) However, ) means flux, and O2 and 302 are gaseous.

Furthermore, the equilibrium represented by the following equation (2) is established between the slag and the metal, and as a result, [51] in the metal is desulfurized and reduced.

[5] + COt)” [01-1-(S2-)
(2) Therefore, we came up with the idea of adding CaS to the flux in advance to replenish the S component. On the other hand, in order to examine the form of sulfur in the slag during ESR, the sulfur in the slag was fractionated and quantified, and the data shown in Table 1 was obtained.

Table 1 As is clear from Table 1, sulfur in the flux is present almost in the form of CaS. This is thought to be due to the low oxygen potential of the slag during electroslag remelting. Therefore, it is expected that if CaS is added in advance as a flux component for ESR, a sufficient amount will be present in the slag, and the tendency to reduce sulfur as described in (1) and (2) above will be avoided. Ta.

(B) CaO: 20-55%, Al2O3: 35-60
%, CaS: 2 to 30% In general, both CaO and Al2O3 have extremely high melting points and have a significant effect on the flux point for ESR.

Therefore, as a result of studies taking this point into consideration, it was found that in order to adjust the melting point of the ESR flux to a suitable value, it was necessary to set CaO: 55% or less and Al2O3: 60%. Nao Ca
The reason for setting the above lower limits for O and Al2O3 is to enable the Ca0-Al2O3-based flux to exhibit its basic action.

Next, regarding CaS, the lower limit was set at 2% because below this, the effect of gas addition, that is, the high yield effect of sulfur in the molten alloy, cannot be achieved. This is because the sulfur content is increased too much.

The Ca0-Al2O3-CaS flux has been explained above, but the sulfur added to the flux is
It is not limited to aS (Canon format is also acceptable, but rather from a cost and practical standpoint, it is CaS).
It is also believed that O4 is preferable. In this case CaSO
If a hydrous type such as 4.2H20 or CaSO4.1/2H20 is used, the [H] concentration in the ingot after ESR will be extremely high, which will result in blowholes at the bottom of the ingot, which is undesirable. of CaSO4 must be used. The following precautions must be taken when using CaSO4 in this manner.

CaSO4 has some oxidizing power and oxidizes the active elements in the steel according to the following reaction (% formula %), and itself is reduced to become CaS. For this reason, as shown in FIG. 1, active elements are reduced, so if the composition specifications for these active elements are strict, it is necessary to reduce CaSO4 to CaS at least in the initial stage of ESR. For this purpose, gold gCa
, Mg, AI.

Oxidizable metals such as Si or their alloys are treated with E in advance.
Ca, Mg, Mn, AI used can be prepared as SR flux or added at the beginning of ESR.
The amount of Si, etc. varies depending on the required quality of the obtained ingot, but is used as a guideline.
2.2/3 nmol of Al for the number n of moles of
The amount is 4 nmol for Ca, Mg, and Mn, and 2 nmol for Si. If the oxidizable metal is added in an amount exceeding these guidelines, there is a risk that the component specifications for the oxidizable metal may be exceeded, so special care must be taken.

As a result of research and examination of CaSO4 from the above points of view, (1) Cab: 20-55%, (2) A1203
:35-60%, (3a) CaSOs :Ca
Fluaflux for ESR that satisfies 2 to 30% in terms of S (1) CaO: 20 to 55%.

(2) A 1203: 35-60%, (3a
) Ca S Os: 2 to 30% in terms of CaS, (3b)
Oxidizable metals or their alloys: It has been found that a high sulfur yield can be achieved by using a flux for ESR that is sufficient to reduce CaSO4 to CaS at least in the initial stage of flux melting. .

In addition, in adjusting each flux explained above, C3LF2 or M g F 2 or CaF2-M
A solvent of gF2'J may be used in some cases, but the optimum amount in this case is preferably 20% or less of the ESR flaflux.

Furthermore, as for impurities such as oxides of Fe and Mn, it is appropriate to limit them to 2% or less in terms of Fe and Mn based on experience.

Each of the ESR fluxes CaO and A explained below
It contains lz 03 , CaS (or CaSO 4 , or an oxidizable metal) as a component, but among these, a part of CaO can be replaced with MgO. That is, if the MgO content was within 10%, ESR could be carried out without any adverse effects on others, but if the MgO content exceeded 10%, not only would MgO-Al2O3 spinel be easily formed, but the melting point of the slack would be significantly lowered. It becomes difficult to perform stable ESR operation as the cost becomes high and the obtained ingot surface deteriorates.

Examples will be explained below.

[Example] ESR was performed in an 80 csφ ESR furnace in an Ar gas atmosphere using the electrode materials shown in Table 2 and the ESR fluff flux having the composition shown in Table 3. Table 3 also shows the yield of sulfur, but as mentioned above! The yields of ingots obtained using ESR flux were all good.

In addition, the above results are comprehensively summarized together with comparative examples in the fourth section.
Shown in the table.

[Effects of the Invention] Since the present invention is configured as described above, it is an object of the present invention to provide a flux for remelting electroslag that can achieve a high yield of sulfur in alloys containing sulfur, such as free-cutting steel. I can do it.

[Brief explanation of drawings]

FIG. 1 is a graph showing the oxidation reduction of active elements at the bottom of the ingot when CaSO4 is used as the sulfur source in the electroslag remelting flux.

Claims (6)

[Claims] (1) A flux used when electroslag remelting a sulfur-containing alloy, the flux having the following properties: [1] CaO: 20 to 55% by weight [2] Al_2O_3: 35 to 60% by weight [3] CaS : 2 to 30% by weight, respectively. (2) Part of the CaO contains Mg within 10% by weight.
The electroslag remelting flux according to claim 1, wherein O is replaced with O. (3) A flux used when electroslag remelting a sulfur-containing alloy, the flux comprising: [a] CaO: 20 to 55% by weight [b] Al_2O_3: 35 to 60% by weight [c] CaSO_4 : A flux for remelting electroslag, characterized in that it satisfies 2 to 30% by weight in terms of CaS. (4) Part of the CaO contains Mg within 10% by weight.
The electroslag remelting flux according to claim 3, wherein O is replaced with O. (5) A flux used when electroslag remelting a sulfur-containing alloy, which flux includes: (a) CaO: 20 to 55% by weight (b) Al_2O_3: 35 to 60% by weight (c) CaSO_4 : 2 to 30% by weight in terms of CaS (d) Oxidizable metal or alloy thereof: For electroslag remelting, characterized in that the amount thereof satisfies the amount necessary to reduce CaSO_4 to CaS. flux. (6) Part of the CaO contains Mg within 10% by weight.
The electroslag remelting flux according to claim 5, wherein O is replaced with O.