JPH07112597B2 - Mold for continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a mold for continuous casting.

<Conventional Technology> Regarding the continuous casting mold, the mold itself is highly durable,
Moreover, many techniques have been developed so far in order to satisfy the requirement that the obtained slab is of high quality. In general, they are provided with a coating layer having excellent wear resistance, such as Ni, on the surface of the mold body, but since this coating layer has poorer thermal conductivity than the mold body, it is thicker near the meniscus. There is a restriction that it can not be done, the vicinity of the lid meniscus part must be rich in heat removal property, and this part is in direct contact with and away from the molten metal, so it will receive an excessive thermal shock This is because if it is too thick, heat cracks will occur.
Therefore, there is a mold in the form of a so-called tapered coating layer in which the thickness of this coating layer gradually increases from the upper part to the lower part of the mold. The applicant of the present invention has also used such a so-called tapered mold for many years.
Even with a mold that has a 1.5 mm thick Ni plating layer at the lower end and a 0.03 mm Cr plating layer on the upper surface to prevent molten metal from sticking, at the lower end after using 600 charges at 300 tons / ch. The copper body was exposed and needed repairs. Although it is thought that such inconvenience will be solved to some extent, the thickness of the Ni plating layer is different between the upper half part and the lower half part of the mold as shown in Japanese Patent Publication No. 61-52238. The thickness of the upper end is 0.3 to 0.5 mm, the lower end is 2.0 to 5.0 mm, and the uppermost layer has a Cr plating layer of about 0.03 mm. In order to cause internal cracking of the cast slab, a method is adopted in which one side is refurbished with wear of about 1.5 mm on one side, and the thick Ni layer at the lower end is restored to the original size to some extent. To be done. However, even with this type of mold, the strength of the boundary between the upper half and the lower half is weak, so the life per campaign is not so long.

<Problems to be Solved by the Invention> The present invention is, of course, that the wear-resistant coating layer is firmly bonded to the mold body in order to solve the problems of the conventional mold. To provide a continuous casting mold capable of significantly improving the durability of the mold as a whole without causing heat cracks or the like even when the coating layer has a thickness sufficient to exhibit wear resistance. The purpose is.

<Means for Solving Problems> The above object of the present invention can be achieved by adopting the following means. That is, a nickel first plating layer is applied to the surface of the copper or copper alloy mold body that is in contact with the molten metal,
A second plating layer made of a nickel-iron-molybdenum alloy is provided on the first plating layer, and the amounts of iron and molybdenum in the second plating layer are gradually increased from the lower layer to the upper layer of the second plating layer. However, the maximum hardness portion is formed at a portion slightly lower than the surface, and conversely from the maximum hardness portion to the surface, the amounts of iron and molybdenum gradually decrease, and the surface hardness of the second plating layer decreases. Is a mold for continuous casting characterized in that it is between the first plating layer and the highest hardness portion.

Even in the present invention, in order to prevent adhesion of the molten metal,
A thin chrome layer may be provided on the uppermost surface of the second plating layer.

<Operation> The continuous casting mold of the present invention has a coating layer (uppermost Cr layer) on the surface of the mold body for improving wear resistance, as compared with the above-described two conventional examples and other conventional molds. However, there is a great feature in that it is provided with a coating layer of one kind rather than a multi-layer of different metals or alloys as in the conventional example or a stepwise difference.
More specifically, what is directly joined to the mold body is the first plating layer made of nickel that is firmly bonded to the mold body, and the second plating layer, which is the upper layer, has iron and molybdenum in addition to the nickel. Is an alloy layer in which the amounts of iron and molybdenum are gradually increased and the hardness thereof is gradually increased. The lowermost part of the second plating layer has a composition similar to that of the first plating layer. It has a composition that is firmly bonded to the plating layer, gradually increases in hardness in the second plating layer, becomes the maximum hardness portion, and thereafter gradually returns hardness slightly. Therefore, the coating layer as a whole will be as if it were a single layer, and since there is no rapid composition change anywhere in the coating layer, the bonding strength is large, and the hardness of the top surface is slightly reduced, so heat cracking occurs. It is also highly durable. Here, the reason why the nickel-iron-molybdenum alloy was selected as the second plating layer is that the hardness of nickel-molybdenum is larger than that of nickel-molybdenum, as described in detail in the section of Examples below. It cannot be thickened. On the other hand, nickel-iron can be thickened up to several mm, but the hardness is insufficient, so in order to make full use of the characteristics of both alloys, a nickel-iron-molybdenum ternary alloy was used. .

<Example> An example of the present invention will be described in detail with reference to the drawings, and a comparative example will be described.

Example As shown in FIG. 1, this example is a Cu mold body (1).
The surface of the lower part of the surface of the
A pure Ni layer (2) is electrodeposited on the entire upper surface to a thickness of about 0.5 mm,
Next, Ni-Fe-Mo alloy layer (3) with a thickness of 1.5 m
The Ni-Fe-Mo alloy layer (3) formed in the m-position electrodeposited form
The ratios of Fe and Mo in the film are changed as shown in FIG. The details of the amounts of Fe and Mo in the Fe + Mo amount in FIG. 2 are as shown in Table 1 below.

The electrodeposition conditions of the mold of this example are as shown in Table 2 below.

The hardness of each part of the coating layer of the mold thus obtained was as shown in FIG.

The results of the actual operation test using the mold of the above example,
300 ton ladle, 2 strand machine could be fully used up to 1300 charge.

In the above embodiment, the second plating layer, that is, the Ni-Fe-Mo alloy layer (3) is provided only on the lower half of the mold body (1), and the upper half is only the first plating layer. Although the heat resistance is enhanced, the second plating layer may be provided on the upper half of the mold body (1) to a thickness that does not impair the heat removal property, if necessary.

Comparative Example Thickness of pure Ni layer over the entire surface of the mold body of the same type as the above example
A mold for continuous casting, which was electrodeposited to 0.5 mm, and then a Ni-Mo alloy layer was electrodeposited only on the lower half under the conditions shown in Table 3 below, and which had a composition and hardness change as shown in FIG. Got

In the mold obtained by this comparative example, the NI-Mo alloy layer as the second plating layer was 0.9 mm shown in FIG.
Even in the case of, there is a microcrack and further thickening is impossible, and it is considered that the hardness becomes large if the amount of Mo is further increased. Therefore, the second plating layer is unsatisfactory in that the thickness and hardness are still insufficient. It was also found that, in actual use, the mold of this comparative example has a durability of not more than about 2/3 of that of the above-mentioned example product due to the occurrence of heat cracks in addition to insufficient wear resistance.

Similarly, in the example of using the Ni-Fe alloy for the second plating layer, it was possible to electrodeposit up to a considerable thickness (about 1.5 mm), but in order to form a good electrodeposition layer, Fe was about 9.8% by weight. It can be contained only up to, and in that case the hardness is about HV = 500 and the wear resistance is still insufficient, compared to the above example products being fully used up to 1300 charges, under 1100 charges under the same conditions Met.

<Effects of the Invention> As described above, according to the continuous casting mold of the present invention, since the coating layer other than the Cr layer is made of one kind of material, and the bottom layer is the mold. Since it is made of nickel that firmly bonds to the main body, there is no peeling due to the large bonding force both inside the mold body and inside the coating layer, and the uppermost part of the coating layer is slightly inside. Since the hardness is slightly lower than that of the lower part, it is also excellent in heat crack resistance and is highly durable as a whole.

Further, the mold of the present invention has the coating layer as described above,
Since it is made of one type of material, the coating can be performed continuously over all of the materials, so compared to the conventional multi-layer coating type mold, the work when applying the coating layer of the same thickness It also has the effect of improving efficiency.

[Brief description of drawings]

FIG. 1 is a perspective view of an essential part of an embodiment of the present invention, and FIG. 2 is the same Ni-Fe.
-A graph explaining the morphology of the Mo alloy layer, and Fig. 3 shows a comparative example.
The graph explaining the form of a Ni-Mo alloy layer. In the figure, (1): Cu mold body (2): Pure Ni layer (3): Ni-Fe-Mo alloy layer

Claims (1)

[Claims] 1. A first plating layer made of nickel is applied to a surface of a copper or copper alloy mold body which is in contact with the molten metal, and a nickel-iron-molybdenum alloy second layer is formed on the first plating layer.
The plating layer is applied, and the amounts of iron and molybdenum in the second plating layer increase gradually from the lower layer to the upper layer of the second plating layer, and the maximum hardness part is formed at a part slightly lower than the surface. The amount of iron and molybdenum gradually decreases from the highest hardness portion to the surface, and the surface hardness of the second plating layer is between the first plating layer and the highest hardness portion. A mold for continuous casting characterized by the above-mentioned structure.