JPH08100223A - Production of high cleanliness steel - Google Patents

Abstract

PURPOSE: To produce a high cleanliness steel, such as cold die steel, steel for cutting tool, and high grade bearing steel, forming large amounts of carbide, having high hardness, reduced in oxygen content, and particularly reduced in oxide inclusions. CONSTITUTION: A molten steel, after Al deoxidation in an electric furnace or in a ladle refining furnace, is subjected to ladle refining and then formed into a cast electrode, and electroslag remelting is done by using this electrode, by which a high C and high Cr steel ingot of <=30ppm oxygen content is obtained. The desirable composition of the high C and high Cr steel ingot consists of, by weight, 0.5-1.6% C, <=1.0% Si, <=1.5% Mn, 10-18% Cr, and the balance Fe with inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to non-metallic inclusions (hereinafter referred to as
The present invention relates to a method for producing highly clean steel with reduced inclusions.

[0002]

2. Description of the Related Art Electroslag remelting method (hereinafter referred to as ES
R) is desulfurization by slag refining, reduction of inclusions, reduction of segregation by layered solidification, reduction of segregation of steel ingot, as compared with a method of ingot casting which is a normal melting method in which it is cast in an ingot case after melting. It has been applied to products that require high reliability because it has many features such as enabling the densification. The consumable electrode used for ESR has conventionally been an electric furnace,
Using what was cast after melting in an induction furnace,
Good quality steel ingots have been obtained by remelting this by the ESR method. Due to the advantages of such products, the melting method by ESR has been widely used in the field of tool steel. In particular, the application of the ESR method reduces the segregation of high-C and high-Cr steels, which have a large amount of carbides such as cold die steel, blade steel, and high-grade bearing steel, and are unique to these steels. Since it has a large effect of uniformly dispersing the carbide, it has attracted attention as an extremely effective melting method as a means for increasing toughness.

[0003]

However, the conventional ES
As a result of investigating the life of the waste materials of the high C and high Cr steel products manufactured by the R method, it is found that not only the cause of the life is not caused by the carbide, but the cleaning is initiated by the oxide-based inclusions. It was recognized that there are many factors related to the degree. As a result of examining the above oxide-based inclusions, that is, a method of reducing cleanliness, factors that affect cleanliness after ESR are roughly classified into (1) ES
R condition and (2) cleanliness of consumable electrode are two. Of these, with regard to (2), it is said that ESR has a small difference between the goodness and badness of the effect of the consumable electrode, as compared with, for example, the vacuum arc remelting method (VAR), but especially the Al ₂ O ₃ system intervenes. The cleanliness of the consumable electrode associated with oxide-based inclusions such as substances has a very large effect on the cleanliness after ESR.

When a consumable electrode that has been melted and refined and cast only in an electric furnace, which has been conventionally used, is remelted by the ESR method, the oxygen level after remelting is high and the cleanliness is very low. There was a problem. On the other hand, conventional E
As a method of improving SR melting, it is effective to reduce S in high-speed tool steel or mold steel for plastic working by ladle refining when melting consumable electrodes of ESR. 111962, JP-A-4-111963.
No. However, these methods have a drawback that the cleanliness of sulfides can be reduced, but the cleanliness of hard and brittle oxides cannot be increased.

An object of the present invention relates to a steel having a large amount of carbides such as cold die steel, blade steel, and high-grade bearing steel as described above, and having a high hardness, and having a low oxygen content, especially an oxide-based inclusion. It is an object of the present invention to provide a method for producing high-purity steel with few substances.

[0006]

Means for Solving the Problems In order to reduce the cleanliness of steel ingots obtained by the ESR method, in particular, oxide-based inclusions, the inventor has to do so at the time of refining in an electric furnace before a ladle refining furnace or at an electric furnace. In order to manufacture consumable electrodes by pouring molten steel that has been smelted in a furnace into a ladle smelting furnace and then deoxidizing it by adding Al, in particular not only increasing the cleanliness of oxide inclusions,
It was found to be extremely effective economically.

That is, according to the present invention, molten steel deoxidized with Al in an electric furnace or a ladle refining furnace is smelted to be a casting electrode, and electroslag remelting is performed using the electrode to reduce the oxygen content from 30 ppm or less. Is a high-C, high-Cr steel ingot. The composition of the steel ingot is C 0.5-1.6% by weight.
%, Si 1.0% or less, Mn 1.5% or less, Cr 1
Steel containing 0 to 18% and the balance Fe and unavoidable impurities, and a part of the above as Mo as a selective addition element,
Each of W is 0 to 0.2% and one or two kinds and 0
A steel obtained by substituting 1 element or 3 elements out of V of 2.0% can obtain a desired effect.

[0008]

The operation relating to the production of the highly clean steel of the present invention will be described below. The features of the method for producing high-purity steel of the present invention are (1) Al deoxidizing a consumable electrode in an electric furnace or A immediately after pouring molten steel in an electric furnace into a ladle refining furnace.
Two points are to add 1 to deoxidize Al, and (2) to smelt deoxidized molten steel in a ladle. As described above, the method for producing high-purity steel of the present invention continuously removes Al-deoxidized steel at the stage of refining steel in an electric furnace or at the initial stage of pouring molten steel after melting into a ladle refining furnace. It is indispensable to refine it in a pot refining furnace and use it for an ESR electrode. This is based on the following experimental facts.

[0009] That is, when ESR is performed after ladle refining of molten steel that has not undergone Al deoxidation, a large difference is observed in the cleanliness of the ESR steel ingot as compared with the case where ladle refining is not performed. On the other hand, as described later in Examples, it was found that the cleanliness of the ESR steel ingot was improved by performing ESR after ladle refining the molten steel deoxidized with Al. These facts show that cleanliness of the consumable electrode is improved by performing Al deoxidation to lower the dissolved oxygen level and further removing the deoxidation product Al ₂ O ₃ in the ladle refining furnace, and Combined with the further refining effect, the cleanliness after re-melting is greatly improved. The timing of adding Al is preferably the final stage of refining in an electric furnace or the initial stage of ladle refining.

The oxygen content in the electrode that has completed the ladle refining is preferably 30 ppm or less, and more preferably 25 ppm or less. Because in the ESR process, the oxide morphology is
Although it can be finely controlled, it is difficult to reduce the oxygen content itself. By satisfying this condition,
It becomes easy to reduce the amount of oxygen after ESR of the present invention to 30 ppm or less. High C and high Cr produced in this way
The steel ingots of the series are, in particular, SKD11, 12 specified by JIS G 4404 (revised 1972) and steels commercially available as improved steels thereof, blade steel containing 10.0 to 14% of Cr, and 10. It is particularly effective for products that contain 0 to 18.0% and have a C% level of 0.5 to 1.5%, such as bearing steel and piston ring materials, that form a large amount of carbide and are heat treated to a high hardness. Is.

The reasons for limiting the desirable composition will be described below. C is one of the effective elements for obtaining the hardness of martensitic stainless steel. In addition to Cr, M
It forms carbides with o, W, V, Nb, etc., and contributes to the improvement of wear resistance. In order to obtain the high strength of the steel of the present invention, at least 0.5% or more is required, but if it exceeds 1.6%, the eutectic carbide becomes coarse and the toughness decreases, so the C range is set to 0.
It is recommended to be 5 to 1.6%. Si is an additional element necessary as a deoxidizing element for steel. However, excessive Si
Since the toughness is remarkably deteriorated, the addition of Al is preferably 1.0% or less. Mn, like Si, is used as a deoxidizing agent, but if the Mn content increases, the retained austenite becomes excessive during quenching and the hardness decreases, so the upper limit is preferably made 1.5%.

[0012] A part of Cr has the effect of forming a solid solution in the matrix to increase the resistance to temper softening, and is also combined with C to form a hard Cr-based carbide, which has the effect of improving wear resistance. In order to obtain the above effect, it is preferable to contain 10% or more. But C
If the amount of r is too large, the eutectic carbide becomes coarse and causes deterioration of toughness, rolling contact fatigue property, etc. Therefore, it is preferable to set the range of Cr to 10 to 18%. These high C and high Cr
In addition to the above desirable composition and steel type, the following elements can be appropriately added to the base steel depending on the purpose of use. Mo: 5
% Or less, W: 2.5%, V: 2% or less, Nb: 1% or less, Ni: 2% or less, Co: 3% or less, of which M
All of o, W, V, and Nb are particularly effective as elements that form carbides with carbon and improve wear resistance.
It is preferable to replace with Fe and add.

The most desirable steel is C 0.65-0.7.
0%, Si 0.20 to 0.50%, Mn 0.6 to 0.
8%, Cr 12 to 13%, C 1.40 to 1.6
0%, Si 0.50% or less, Mn 0.6% or less, Cr
11-13%, Mo 0.8-1.2%, V 0.2-
Examples include 0.5%.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments.
Steel having a composition range shown in Table 1 was electromelted (EF). Among these, in the method of the present invention, Al was added at the time of EF dissolution to deoxidize Al, and was poured into a ladle refining furnace (ASEA) to obtain a consumable electrode after refining. On the other hand, the comparison method EF
Immediately thereafter, Al deoxidation was not carried out for the consumable electrode.

[0015]

[Table 1]

FIG. 1 shows a comparison of cleanliness of materials manufactured in each manufacturing process, and the cleanliness is represented by an index of the number of inclusions. However, in any case, various conditions in ESR are constant. EF-ES after EF-ASEA-ESR
Compared to after R, inclusions were generally small, and the tendency was strong especially for inclusions having a relatively small size of 10 μm or less. It has been confirmed by EPMA that the inclusions are mainly spherical Al ₂ O ₃ -based inclusions. It is considered that the cleanliness of the consumable electrode is improved by performing ladle refining during the melting of the consumable electrode, and as a result, the cleanliness after ESR is improved. In order to confirm this, FIG. 2 shows a result of comparison of cleanliness of the consumable electrode before ESR, and it can be seen that there is a large difference in cleanliness at the time of melting the consumable electrode. Therefore, it is clear that the difference in cleanliness of the consumable electrode has a great influence on the cleanliness after ESR.

Next, FIG. 3 shows the relationship between the oxygen content after ESR and the distribution of inclusions. The cleanliness after ESR correlates with the oxygen content, and the cleanliness deteriorates as the oxygen content increases. There is. This tendency is particularly strong in EF-ESR that is not ladle refined. FIG. 4 shows changes in oxygen content before and after ESR in order to understand deoxidation behavior in ESR. In the case of EF-ESR, although the deoxidation rate is relatively high, the oxygen level of the original consumable electrode is high,
The subsequent oxygen level is also high, which adversely affects cleanliness. Further, it can be seen that the EF-ESR has a larger variation in oxygen level.

[0018]

The steel ingot obtained by the method of the present invention is
By lowering the oxygen content, a higher degree of cleaning can be achieved, and in particular, hard and brittle oxide-based inclusions such as Al ₂ O ₃ are reduced. As a result, when a large amount of carbides such as cold dies, blades, and high-grade bearing steel are formed, and when used in high C and high Cr type products where the hardness of the base itself is high, the cause of chipping and large cracks is a major factor. The effect is remarkably large.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a manufacturing process and distribution of inclusions.

FIG. 2 is a diagram showing a relationship of distribution of inclusions of consumable electrodes.

FIG. 3 is a diagram showing the relationship between the amount of oxygen and distribution of inclusions after ESR.

FIG. 4 is a diagram showing changes in oxygen content before and after ESR.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C22C 38/24 (72) Inventor Kiyotaka Kochio 2107 Yasugi-cho, Yasugi-shi, Shimane Prefecture 2 Hitachi Metals Shares Company Yasugi factory

Claims (2)

[Claims] 1. A molten steel, which has been deoxidized with Al in an electric furnace or a ladle refining furnace, is subjected to ladle refining and then used as a casting electrode, and electroslag remelting is performed using the electrode to obtain an oxygen content of 30.
A method for producing highly clean steel, which comprises obtaining a steel ingot of high C and high Cr content of not more than ppm. 2. A high-C, high-Cr steel ingot, in% by weight, containing C
0.5-1.6%, Si 1.0% or less, Mn 1.5%
Hereinafter, steel containing Cr of 10 to 18% and the balance of Fe and unavoidable impurities, or Mo and W of 0 to 0.2% each with a part of Fe as a selective additive element
The method for producing a highly clean steel according to claim 1, wherein the steel is a steel obtained by substituting 1 element or 3 elements from among 2 kinds or 2 kinds and V of 0 to 2.0%.