JPH05277666A - Continuous cast slab of fe-cu alloy - Google Patents

Abstract

PURPOSE:To provide a thin cast slab which is the Fe-Cu alloy having a composition consisting of Cu at the ratio of the specified range, whose thickness is in the specified range, and where cracking flaws are difficult to be generated during the cooling after casting. CONSTITUTION:A cast slab has the composition consisting of, by weight, 20-90% Cu and 1-10% Cr, or further <=10% in total, of one or two or more elements selected among Mo, Al, La, Si, Ti, Zr, C and B, and the balance substantially >=10% Fe, and the surface layer part of the cast slab is formed by the columnar structure whose thickness is >=1/3 of the thickness of the cast slab. The cast slab is >10mm and up to 80mm in thickness.

Description

Detailed Description of the Invention

[0001]

The present invention relates to Cu of 20 to 90% by weight.
The present invention relates to a continuously cast slab of an Fe-Cu based alloy contained. This continuously cast slab of Fe-Cu alloy can be rolled into a thin plate and used as a material for electronic or magnetic parts, for example, a lead frame material.

[0002]

2. Description of the Related Art For example, Japanese Patent Application No. 2-93440 and Japanese Patent Application No. 3-73265 are inventions related to the application of the present inventors, which describe an Fe--Cu alloy thin plate using continuous cast slabs. Has been done. That is, a continuously cast slab having a fine metal structure and a thickness of 2.2 to 10 mm is manufactured by specifying the alloy components, and the slab is cold-rolled to manufacture a Fe—Cu alloy thin plate.

According to the knowledge of the inventors of the present invention, the slab of the Fe-Cu alloy immediately after casting has a low strength, so that the thermal stress generated in the slab during cooling causes cracks on the surface of the slab. There is a problem that it easily occurs. If the composition of the molten metal is selected within the composition range described in Japanese Patent Application No. 2-93440 and Japanese Patent Application No. 3-73265, this problem will be ameliorated a little and continuous cast slabs with a thickness of 10 mm or less can be produced. Becomes

However, it is difficult to sufficiently prevent the cracks from cracks only by selecting the components. Therefore, cracks frequently occur in a slab having a thickness of more than 10 mm which causes a large thermal stress during cooling of the slab. In addition, it has not been manufactured in the past.

[0005]

Fe-Cu alloys as materials for electronic and magnetic parts are often used as thin plates having a thickness of 0.5 mm or less. Therefore, the thickness is 2.2
It can also be manufactured by rolling a 10 mm slab. When manufacturing a thin slab, the casting speed (m / min) is increased and continuous casting is performed at a high speed. However, since the thickness is thin even if cast at high speed, the productivity (ton / min) of continuous casting is small with the conventional slab having a thickness of 2.2 to 10 mm, and continuous casting is performed with high productivity. Things are difficult.

If a slab having a thickness of more than 10 mm can be produced without causing cracks during cooling, the productivity of continuous casting is greatly improved. The present invention has an F of 10 mm or more.
It is an object of the present invention to provide a cast slab of an e-Cu alloy that is resistant to cracking during cooling.

[0007]

According to the present invention, Cu is added in an amount of 20 to 20%.
90% by weight and 1 to 10% by weight of Cr, or 10% by weight or less in total of one or more elements selected from Mo, Al, La, Si, Ti, Zr, C and B, Moreover, the balance relates to a continuously cast slab having a composition of 10 wt% or more of Fe and having a thickness of more than 10 mm to 80 mm.

The Fe-Cu alloy of the present invention contains at least 20% by weight of Cu in order to improve electric conductivity and heat dissipation as a material for electronic and magnetic parts. Fe in alloy
Although the amount imparts strength to the alloy, if the Cu content exceeds 90% by weight, the Fe content becomes too small and the strength becomes insufficient. C
The proportion of the content of u and the content of Fe is selected according to the application based on the balance between electrical conductivity and the strength, but Fe is contained in an amount of 10% by weight or more.

Cr is contained in order to impart corrosion resistance to the alloy. If it is less than 1% by weight, the improvement effect is small, so 1% by weight or more is contained. However, when Cr is contained, coarse crystal grains are likely to be generated in the cast slab. Therefore, the content is 10% by weight or less.

Although not essential in the present invention, it is possible to further contain one or more elements selected from Mo, Al, La, Si, Ti, Zr, C and B in a total amount of 10% by weight or less. it can. Mo imparts corrosion resistance to the alloy similarly to Cr, and Al, La, Si, Ti, Zr, C, B
Prevents the formation of coarse crystal grains in the slab. However, if these elements are excessively contained, the total content of Cu and Fe decreases, and the electric conductivity and strength of the Fe—Cu alloy are impaired. Therefore, the total content is 10% by weight or less, preferably 5% by weight or less.

FIG. 2 is an explanatory view of an example of a twin belt type continuous casting apparatus. 4 is a metal belt stretched between the pulleys 1, 2 and 3 and runs in the direction of the arrow. The metal belt 4'also runs while being stretched between the pulleys 1 ', 2', 3 '. The metal belts 4 and 4'are opposed to each other as shown in FIG. 2, and the sections 1 and 2 and the sections 1'and 2'are arranged substantially parallel to each other and run.

Between the metal belts 4 and 4'running in parallel, side weirs (not shown) are arranged at both ends of the metal belt (upper end of paper and lower end of paper). The molten metal 7 is poured into the space formed by the metal belts 4, 4'and the side weirs running in parallel. The poured molten metal forms solidified shells 6 and 6'on the metal belt, and the solidified shells 6 and 6'follow the running of the metal belts 4 and 4'and move downward to form a slab 8. Taken out. By using the twin-belt type continuous casting apparatus of FIG. 2, a continuously cast slab having a thickness of more than 10 mm to 80 mm can be manufactured with high productivity.

The slab of the present invention is characterized in that the surface layer portion of the slab is formed with a columnar structure having a thickness of ⅓ or more of the thickness of the slab. That is, for example, in the case of a slab having a thickness of 30 mm, a columnar structure having a thickness of 10 mm or more is formed on the surface layer portion of the slab. In the present invention, the columnar structure means that the cross-section of the cast slab is polished with alumina and the polished surface is H ₂ O: 50.
cc, HNO ₃ : 25 cc, acetic acid: 25 cc solution 1
It refers to a gathered portion of a stretched metallographic structure that is seen from the surface of the slab toward the center of the thickness of the slab, which is observed when macro-etching is visually performed for 1 to 2 minutes.

As will be described in detail later, a cast product in which the surface layer portion of the cast product has a columnar structure having a thickness of 1/3 or more of the thickness of the cast product has, for example, a Cu content of about 50%. , Fe content is about 50% and Cr content is 0.5%, the temperature of the molten metal injected into the twin-belt type continuous casting apparatus in FIG. It is obtained by controlling to. When the temperature of the molten metal having this composition is, for example, 1300 ° C. or lower, no columnar structure is observed in the surface layer of the cast piece, and the entire cross section becomes a cast piece formed of only the granular structure.

[0015]

OPERATIONS AND EXAMPLES The present inventors manufactured the Fe--Cu alloy cast pieces shown in Nos. 1 to 4 of Table 1 by the twin belt type continuous casting apparatus shown in FIG.

The slab was cold-rolled and visually inspected for cracks. According to the knowledge of the present inventors, cracks with a length of 50 mm or less have a shallow depth and can be easily removed by care, which does not cause a great obstacle in the rolling in the post-process, but the length exceeds 50 mm. It is difficult to remove the cracks. Therefore, in Fig. 1, a slab with a crack length of over 50 mm was used without cracks, and a crack with cracks had a length of 50 mm.
It refers to a slab that had a crack.

[0017]

[Table 1]

The inventors of the present invention also took a sample for macro etching of a transverse cross section from a substantially central portion in the length direction of each cast piece, and investigated the thickness of the columnar structure in the surface layer portion of the cast piece. The thickness of the columnar structure of the slab and the observation result of the crack of the slab are shown in FIG.

As shown in FIG. 1, when the columnar structure is thin and {(columnar structure thickness) / (cast piece thickness) × 100} is 20 or less, all the cast pieces have cracks, which is an extreme case. Is broken. On the other hand, {(columnar structure thickness) / (cast piece thickness) × 100} is 3
In the case of 0 or more, cracks did not occur on the cast piece.

The present inventors further investigated the metallographic structure of these cast pieces, and obtained the following findings. That is, in the vicinity of the crack of the slab in which the crack is generated, a huge abnormal structure having a size of about 3000 μ or more is scattered in the surface layer portion of the slab within 1/3 of the thickness of the slab. This huge abnormal structure is not observed in the columnar structure, and is scattered exclusively in the structure of granular crystals. Therefore, the surface layer of the slab is 1/3 of the thickness of the slab.
The slab formed of the columnar structure having the above thickness does not have a huge abnormal structure in the surface layer portion of the slab, and the slab does not break or crack.

The reason why a huge abnormal structure is generated exclusively in the structure of granular crystals and not in the columnar structure is not necessarily clear, but the present inventors consider as follows.
As mentioned above, Cu: about 50%, Fe: about 50%, C
When a molten metal of r: 0.5% is cast at 1300 ° C., the whole becomes a slab with a structure of granular crystals, but a large number of huge abnormal structures are observed in the surface layer of this slab.

FIG. 5 is a phase diagram of a known Fe-Cu.
A molten metal having a composition of Cu: about 50%, Fe: about 50%, Cr: 0.5% and a temperature of 1300 ° C. is shown as a state of FIG. That is, the molten metal in (a) is in a (melt + γ) state, and the molten metal before casting contains particles of γ which have already solidified in a floating state. During the solidification of the melt, each floating γ particle serves as a nucleus to grow crystals. Therefore, the whole structure is a free crystal structure.

The molten metal reaches a temperature near 1080 ° C. and completes solidification. However, since the molten metal in (a) is a mixture of γ particles and a melt, the melt fills the gaps between the γ particles and solidifies when solidified. However, it becomes a ε phase of a huge abnormal structure and is scattered in the vicinity of the surface layer of the slab.

As mentioned above, when this molten metal is cast at 1450 ° C. or higher, it becomes a slab having a columnar structure.
No huge abnormal structure is observed in the surface layer of this slab. In FIG. 5, B is an example of this molten metal. This molten metal is γ before casting
After being injected without containing the particles of, the temperature near the liquidus line is reached and nuclei of γ are generated. The molten metal is cooled most quickly at the contact portion with the metal belt and reaches the temperature near the liquidus line.
Therefore, nuclei of γ are first generated in a portion corresponding to the surface layer of the slab, and when the temperature drops, the nuclei of γ grow dendriticly toward the center of the slab in the thickness direction.

Therefore, a columnar structure having directionality can be obtained. As the nuclei of γ grow into dendrites, the melt is trapped between the dendrites and reaches near 1080 ° C to solidify,
The melt trapped between the dendrites is fine, so the solidified ε phase is fine and does not form a huge abnormal structure.

In the slab having insufficient columnar crystal thickness, a huge abnormal structure is scattered on the surface layer of the slab. The large abnormal structure has a high Cu content and a small strength ε phase. Therefore, the cast piece causes cracks starting from this abnormal structure. The slab with sufficiently thick columnar crystals does not have a huge abnormal structure in the surface layer, and the ε phase is finely and uniformly dispersed. Therefore, the material strength is uniform, and since there is no defect that is the starting point of cracks, cracks are less likely to occur.

In FIG. 5, Cu: about 50%, Fe: about 50%
However, in the case of melts of other components as well, when the melt above the liquidus temperature is poured into the pool of the continuous casting equipment, the surface layer of the cast slab is ⅓ of the thickness of the cast slab. It is possible to obtain a slab formed of a columnar structure having the above thickness.

FIG. 3 is a slab having a columnar structure with a thickness of ⅓ or more of the thickness of the slab prepared by the present inventors for the Fe--Cu based alloy containing 3% of Cr. FIG. 3 is a diagram showing an example of the temperature of the molten metal during the casting of the cast iron. By using the molten metal having a temperature higher than that shown by the dotted line, the cast piece having the columnar structure of the present invention can be obtained. FIG. 4 shows Fe-containing 6% of Cr.
An example of a Cu-based alloy is used in the same manner as in FIG. 3 to obtain a cast slab having the columnar structure of the present invention.

As described with reference to FIGS. 3 to 5, when the composition of the molten metal changes, the lower limit temperature of the molten metal required for producing the cast product having the columnar structure of the present invention changes, but this lower limit temperature It is easy to grasp in advance by experiments and the like, and by maintaining the temperature of the molten metal at a temperature higher than this lower limit temperature, the cast piece having the columnar structure of the present invention can be easily obtained.

The present invention has been described above with respect to the cast piece produced by the twin belt type continuous casting apparatus of FIG. 2. The effect of the cast piece of the present invention is to control the casting temperature based on the new metallurgical findings of the present invention. By doing so, it can be easily obtained in the case of other continuous casting equipment. Therefore, the present invention is not limited to the slab produced by the twin belt type continuous casting apparatus, and the present invention includes all slabs of the Fe-Cu alloy having the properties limited by the present invention.

[0031]

EFFECTS OF THE INVENTION By using the continuously cast slab of the Fe-Cu alloy of the present invention, it is possible to prevent the occurrence of cracks and fractures when it is conveyed to a coiler after casting or wound by the coiler. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the columnar structure of the slab and cracks / fractures, FIG. 2 is an explanatory diagram of a twin belt type continuous casting device, and FIG. 3 is C
The figure which shows the example of the molten metal temperature suitable for manufacturing the cast piece of the Fe-Cu type alloy of this invention which contains 3% of r. FIG. 4 shows the Fe-Cu type alloy of this invention which contains 6% of Cr. The figure which shows the example of the molten metal temperature suitable for manufacturing a cast piece, FIG. 5: Fe-Cu
It is a state diagram.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazumi Yasuda 20-1 Shintomi, Futtsu City, Chiba Shin Nippon Steel Co., Ltd. Technical Development Division (72) Inventor Satoshi Nishimura 20-1 Shintomi, Futtsu City, Chiba Prefecture New Japan (72) Inventor Kosaku Shioda 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Co., Ltd. Technical Development Headquarters (72) Kenichi Miyazawa 1 Kimitsu, Kimitsu-shi, Chiba Shin-Nihon Kimitsu Steel Works, Ltd.

Claims (1)

[Claims] 1. A Cu content of 20 to 90% by weight and a Cr content of 1 to
10% by weight, or further Mo, Al, La, S
i, Ti, Zr, C, B containing 1 or 2 or more elements in a total amount of 10% by weight or less, and the balance of 10% by weight or more of Fe, and having a thickness of more than 10 mm to 8 mm.
A continuous cast slab of 0 mm, wherein the surface layer portion of the slab is formed of a columnar structure having a thickness of 1/3 or more of the thickness of the slab, a continuous Fe-Cu alloy Casting slab