JP2003293027A - Method of producing calcium free-cutting stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of producing calcium free-cutting stainless steel in which a variation in yield in the addition of Ca is reduced and oxide based inclusions useful for machinability are formed, and which has high machinability in the production of calcium free-cutting stainless steel having increased machinability by the incorporation of ≥0.0020 wt.% Ca. <P>SOLUTION: FeSi of ≤0.1%, ordinarily, about 0.05% is added to the molten metal of stainless steel to insufficiently interrupt deoxidation, and a CaSi wire is fed in a state where a large quantity of O is present to form a large quantity of CaO. After that, FeAlSi is added thereto, and the remaining deoxidation is performed, and further, SiO<SB>2</SB>and Al<SB>2</SB>O<SB>3</SB>are formed, so that oxide based inclusions in the steel are made enough in gehlenite 2CaO-SiO<SB>2</SB>-Al<SB>2</SB>O<SB>3</SB>or anorthite CaO-Al<SB>2</SB>O<SB>3</SB>-2SiO<SB>2</SB>, and particularly enough in gehlenite. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing calcium free-cutting stainless steel, more specifically, by improving the machinability improving effect by controlling the composition of oxide inclusions present in the steel. The present invention relates to a method for producing calcium free-cutting stainless steel.

[0002]

2. Description of the Related Art Since typical austenitic stainless steels, SUS304 and SUS316, are often made into parts by machining, their machinability is improved to produce free-cutting stainless steel. . There are various means for improving the machinability of this type of steel, but the addition of calcium is effective.

[0003] mechanism of improving the machinability of calcium free cutting stainless steel, _the anorthite _{CaO · Al 2 O 3 · 2SiO} 2 or gehlenite 2CaO · _Al 2 O3 is a ternary compound as oxide inclusions in steel · SiO ₂ is produced, because they are compounds having a low melting point, to adhere to the tool to melt during cutting, it is believed that the lubricating effect on the tool. In the ternary system phase diagram of FIG. 1, region I is a grenite and region II is an anorthite generation region. Of these two types of composite inclusions, gehlenite has a lower melting point (1 against 2100 ° C for anorthite).
580 ° C.), which is more preferable from the viewpoint of the machinability improving effect.

The Applicant has sought a method for producing the above-mentioned low melting point compound in stainless steel, added Ca and Al in predetermined amounts, and regulated the amount of O by Ca /
A technique has been established and disclosed in which at least 20% of oxide-based inclusions are made into gehlenite by maintaining the atomic ratio of O and Al / O above a certain value (JP-A 06-1459).
08). Furthermore, the Applicant has prepared a binary or ternary oxide complex or mixture for providing the above complex inclusions in the form of premelt in order to ensure that the above inclusions are present in the stainless steel, and prepares them in the molten metal of the stainless steel. The technique of adding was also developed and disclosed (Japanese Patent Laid-Open No. 09-31014).
4).

As described above, of the two types of composite inclusions, since gerenicite is more preferable than anorthite, it goes without saying that it is desired to increase the production ratio thereof. Further, it goes without saying that it is desirable that these complex inclusions, particularly gehlenite, are produced during the refining process of stainless steel and are dispersed in the steel.

[0006] In the conventional method for producing calcium free-cutting stainless steel, stainless steel is melted in a conventional AOD furnace, and about 0.3% of Si is added at the end of the chromium reduction for deoxidation. At this time, Al is also added to
Also deoxidation by. (The contribution rate to each deoxidation is
Approximately 80% Si and 20% Al are measured. ) Then, Ca is added to generate the above oxide inclusions. Ca is usually added by continuously pushing CaSi wires into the molten metal.

However, as is well known, Ca
Is a substance with a low specific gravity and a low melting point / boiling point,
When added, it diffuses into the slag and volatilizes,
The yield of addition to steel is not good. In addition, in actual operation, as shown in FIG. 1, the addition yield varies widely, and it is often experienced that the Ca content is significantly different even with the same wire supply amount. In order to improve the machinability by adding Ca, that is, in order for the above-mentioned composite inclusions to have the effect of increasing the machinability, Ca is added to steel in an amount of 200
It has been confirmed that it is necessary to be present in ppm (0.002%) or more. To meet this condition, a large amount of CaSi wire must be supplied.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems in the production of calcium free-cutting stainless steel, to reduce the variation in Ca addition yield, and to use oxide inclusions useful for machinability. It is an object of the present invention to provide a method for producing calcium free-cutting stainless steel which has a high machinability and which is produced by a large amount of gehlenite and anorthite, especially the former.

[0009]

The method for producing calcium free-cutting stainless steel according to the present invention, which achieves the above-mentioned object, comprises C
a: A method for producing a stainless steel having an improved machinability by containing 0.0020% (weight) or more,
Normally, 0.1% or less of Si is added to the molten metal of stainless steel melted using an AOD furnace to perform insufficient deoxidation, and Ca is added in the presence of a large amount of O. After producing a large amount of CaO, Si and Al are added to perform the remaining deoxidation and SiO ₂ and Al ₂ O ₃
Is generated, the oxide-based inclusions in the steel are enriched in gehlenite 2CaO.SiO ₂ .Al ₂ O ₃ or anorthite CaO.Al ₂ O ₃ .2SiO ₂ .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION To add Si for incomplete deoxidation, a low Al type FeSi alloy may be added. At this stage, deoxidation with Al is not yet performed.
The amount of Si needs to be 0.1% or less, and is usually 0.
About 05% is suitable. Ca may be added by pushing in a CaSi alloy wire as in the conventional method. If the added amount is too large, desulfurization may occur due to the binding of Ca and S, and the amount of S in steel may decrease.
The main role of improving the machinability of calcium free-cutting steel is oxide inclusions, but MnS brought by S also enhances the machinability through a mechanism common to many free-cutting steels. Extreme desulfurization should be avoided. As described above, when the Ca content is 0.002% or more, the effect of addition becomes clear, and when it exceeds 0.003%, a saturation tendency is exhibited, so it is a good idea to stop it at about 0.005%.

The addition of Si and Al to complete the deoxidation can also be carried out by adding a FeAlSi alloy, which is a known means. The salt brilliance of the slag is reduced to about 1.6 in the conventional refining method in which Al deoxidation is performed from the beginning, but is maintained at a height of about 20, in the incomplete deoxidation step of the present invention. This is an undesirable product of manganese
This is to prevent the formation of chromate MnO.Cr ₂ O ₃ .

After all, deoxidation by Si is a means of adding only Si initially and then adding Ca as a CaSi wire (usually, Si accounts for 30% of the wire),
And the final addition as FeAlSi alloy over three steps. It suffices that the total of these Si amounts provides sufficient deoxidation together with the contribution of Al added together to deoxidation.

As mentioned at the outset, the origin of the present invention is
Austenitic stainless steel SUS30 and SU
It is to develop a free-cutting type of S316, and these steel types are still important as objects to which the present invention is applied. However, deoxidation by Si and Al is performed, and Ca-based inclusions of Ca The present invention is also applicable to steel types other than these, such as ferritic, austenitic-ferrite dual-phase and martensitic stainless steels, as long as the machinability is improved by utilizing.

[0014]

Example Five kinds of stainless steels were manufactured by the following manufacturing method. (1) Normal (non-free cutting type) SUS304: Following melting in an arc furnace, chromium reduction in an AOD furnace and component adjustment in a ladle refining furnace. (2) Calcium free-cutting type SUS304 (prior art): In the manufacturing method of 2) above, FeAl was used in a ladle refining furnace.
Si reduction (Si: 0.3%) and Ca addition by CaSi wire supply. Ca content is A: 0.00
12%, B: 0.0020%, C: 0.0031%. (3) Calcium free-cutting type SUS304 (Example of the present invention): Fe in a ladle refining furnace in the manufacturing method of 2) above
Si reduction (Si: 0.05%), Ca addition by CaSi wire supply and final reduction by FeAlSi alloy (Ca content 0.0036%).

The oxide inclusions of these stainless steels were analyzed to measure Ca / O and Al / O, and the corresponding points of both were plotted to obtain the graph of FIG. FIG. 3 is substantially the same as the graph shown in the above-mentioned JP-A-06-145908, in which the above (1) steel in which no means for improving the machinability was taken, and the amount of Ca added was 0.0012%. to in perching (2-a) steel, oxide inclusions is a _CaO-Al 2 _{O 3} mainly
Almost no ternary compounds exist, and C
In (2-B) steel with a of 0.0020%, Ca / O and A
It can be seen that the points corresponding to 1 / O are in the anorthite region, and in the (2-C) steel in which Ca is 0.0031%, they are in the gehlenite region.

Since the manufacturing method of the present invention carried out 5 charges, the results of each charge are plotted in FIG.
The point where O and Al / O corresponded to each other was in the region where oxide inclusions rich in gehlenite were formed, except for the exception of one charge.

Next, the above five kinds of stainless steels were turned under the following conditions, and the wear condition of the tools with the passage of cutting time was examined. The result is shown in the graph of FIG. Tool: Carbide “P20” Feed: 0.15 mm / rev Speed: 150 m / min Lubricant: None

The data of FIG. 4 shows that when calcium free-cutting SUS304 was manufactured by the conventional technique, the effect of improving the machinability was poor when the Ca content was 0.0012%, and the addition amount reached 0.0020%. The effect is recognized, but the effect of addition does not increase so much even if the amount of Ca is increased to 0.0031%. On the other hand, according to the present invention, the preferred oxide-based inclusion, gerenic, becomes rich. It can be seen that the machinability improving effect is further enhanced if the conditions are given.

[0019]

EFFECTS OF THE INVENTION If calcium free-cutting stainless steel is manufactured according to the manufacturing method of the present invention, that is, Si deoxidation at the final stage of chromium reduction is intentionally stopped insufficiently, and Ca in a large amount of O remains. By adding CaO to produce CaO, and then complete deoxidation with Si and Al to produce oxides thereof, a ternary system, which is a preferable oxide-based inclusion, particularly a steel rich in gerenicite, is obtained. Since it is obtained, it is possible to provide the stainless steel having high machinability by enjoying the excellent free-cutting effect.

As described above, adding Ca to the molten metal of stainless steel is a work which suffers from a low addition yield and a large variation. The addition of Ca in the production method of the present invention, specifically the indentation of the CaSi wire, causes a considerable portion of the added Ca to be C due to the high O concentration.
As a result of being oxidized to aO, the yield tends to be low, but it is not inferior to the conventional technique. More importantly, the yield variation is small, and Ca required for ensuring the machinability improving effect is:
The advantage is that it is easy to achieve the condition of 0.0020% or more.

[Brief description of drawings]

FIG. 1 is a CaO—Al ₂ O ₃ —SiO ₂ ternary phase diagram.

FIG. 2 is a bar graph showing variations in Ca content in molten metal in the production of calcium free-cutting stainless steel.
The upper and middle rows are according to the prior art, and the lower row is an embodiment of the present invention.

FIG. 3 is a graph showing the component balance and composition of oxide inclusions in free-cutting or non-free-cutting stainless steel.

FIG. 4 is a graph showing the relationship between the cutting time and the average tool wear amount of free-cutting or non-free-cutting stainless steel.

Claims (3)

[Claims] 1. A method for producing a stainless steel having an improved machinability by containing Ca: 0.0020% (weight) or more, wherein the content is 0.1% with respect to the molten metal of the stainless steel.
The following Si is added to perform insufficient deoxidation, and a large amount of O
In the presence of Al, Ca is added to generate a large amount of CaO, and then Si and Al are added to perform the remaining deoxidation and SiO ₂ and Al ₂ O ₃ are generated, thereby oxidizing the steel. Material inclusions are Gerenite 2CaO
・ SiO ₂・ Al ₂ O ₃ or anorthite CaO ・ A
method for producing a calcium free cutting stainless steel which is characterized in that as rich in l ₂ O ₃ · 2SiO _2. 2. The addition of Ca is carried out by pushing a CaSi alloy wire, and the addition of Si and Al is performed by FeAlS.
The manufacturing method according to claim 1, which is carried out by adding an i alloy. 3. The method according to claim 1, wherein the stainless steel is austenitic stainless steel SUS30 or SUS316.