JPS6076252A - Double layer cast iron mold for steel ingots - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cast iron mold for steel ingots, and more specifically, the present invention relates to a cast iron mold for steel ingots. Concerning cast iron molds for ingots.

In recent years, during ingot making of rimmed steel and killed steel, ingot making methods such as raising the ingot injection temperature and discontinuing the application of steel refining agents to the inner surface of the mold have been adopted for the purpose of improving the quality of the steel ingot.

By the way, when molds used under these conditions are injected with molten steel and the steel ingot is pushed out of the mold after a certain period of time,
As shown in Figure 1, a part of the lower part of the mold (1) is
) and are likely to be punched out together with the mold, resulting in a defective part (3) at the bottom of the mold. This phenomenon is caused by the tone sheet (TORN 5EAT
), and has the characteristic that it occurs less than about 10 times after the mold is used. FIG. 2 is a diagram illustrating the generation of the i\tI tone sheet, and shows a defective part (3) formed by hollowing out a part of the fiQ mold (1) on the inner surface of the lower part of the mold.

If the above-mentioned tone sheet occurs, and if the defect at the bottom is large, it is impossible to reuse the mold, and even in the case of a slight defect, the upper part of the defect is cut transversely, and the defect is shortened to the standard size. It had no choice but to be used as a mold for short steel ingots.

The present invention has been made in view of the above problems, and its purpose is to provide a cast iron mold for steel ingots that does not generate tone sheets. At least in the lower part of a cast iron mold for steel ingots where tone sheets are likely to occur, the inner layer of the mold is in contact with molten steel.The inner layer from 2 to 1 is made of a ferrous material with a low yield point, and the outer layer is made of graphite. is uniformly dispersed, the base is made of cast iron material, and the inner layer and outer layer are metallurgically integrated.

Below, we will discuss the causes of the tone sheet, and
The configuration of the present invention will be explained in detail.

First, the cause of the occurrence of the tone sheet is considered to be as follows.

1. In the case of a top cast ingot, the poured molten steel falls onto a surface plate set at the bottom of the mold, scatters and hits the inner surface of the bottom of the mold.

2. Even after the injection of molten steel is completed, the impact force due to the convection of molten steel and the static pressure of the molten steel head act on the inner surface of the mold.

8. The higher the injection temperature of the molten steel, the greater the effect of these factors.In addition, the steel refining agent has the function of protecting the inner surface of the mold during ingot making, so if it is discontinued, The influence of molten steel on the inner surface of the mold is extremely large.

4. For the above reasons, welding between the inner surface of the lower part of the mold and the molten steel is unavoidable.

5. When pushing out the welded steel ingot from the mold, the static pressure from above is as shown in Figure 3, with the welded part (4) as the stopping point,
A diagonal downward force acts from the steel ingot (2) to the mold (1), causing damage to the inner surface of the lower part of the mold as described above.

In view of the above points, in order to prevent the generation of force acting diagonally downward on the mold (1), at least the inner layer of the lower part of the 'a shape where tone sheets are likely to be formed is made of a material with a low yield point, and If the mold is rubbed, the effect during punching out of the steel ingot is only slight peeling of the inner layer (so-called rough skin), and the occurrence of fi)-n sheets can be prevented.

FIG. 4 shows the substructure of the composite mold according to the above description. In the figure, (5) is the outer layer of the mold, and (6) is the inner layer.

The outer layer (5) is made of the same material as the conventional ordinary cast iron mold material, which has excellent resistance to thermal stress generated during ingot making. That is, it has a graphite structure with a uniform shape distribution, and
A homogeneous pearlite structure is formed over the entire outer layer as a base structure.

The inner layer (6) is formed to have a layer thickness of 0.5 to 1 fl, and is made of cast iron with a ferrite base. If the number is less than 0.5, the effect of preventing the occurrence of tone sheets is insufficient, and even if the number exceeds 11, the preventive effect remains the same. This fezite fabric is the outer layer (5
) is metallurgically integrated with the barfit area.

Microscopic photographs of the outer layer (5) and the inner layer (6) are shown in FIG. 5 and FIG. 6. Figure 5 is a micrograph (xloo) showing the structure of the outer layer (6) located 1.5 m from the inner surface of the mold, in which graphite is uniformly dispersed in the barfit base.
It shows. In addition, the right side in the figure shows the inner side of the mold. On the other hand, FIG. 6 shows a micrograph (xloo,) near the boundary between the mold outer layer (5) and the inner layer (6). In FIG. 6, the right half shows the inner layer (6), where it is observed that graphite is uniformly dispersed in the ferrite base.

In addition to Figures 5 and 6, please refer to Figures 7 and 8 for reference.
The figure shows a micrograph (xloo) of a conventional ordinary cast iron mold. FIG. 7 shows the structure at a position 1.5M from the inner surface of the mold, with the right side showing the inner surface, and FIG. 81 showing the structure near the inner surface of the mold. It can be seen from the figures in Figures 7 and 8 that graphite of approximately the same shape is uniformly distributed in the pearlite base. However, in FIG. 8, the right end of the photograph shows the inner surface of the mold, and deformation of the structure due to molten steel can be seen.

In short, the method for manufacturing the cast iron mold having the two-layer structure of the present invention described above will be described.

First, to outline an example of a casting method for producing a mold for steel ingots, as shown in Fig. 9, a flat lower mold (8
) A core mold (9) that forms the desired inner surface of the mold is erected, and the core mold (9) is surrounded and spaced at regular intervals to form the desired wall thickness of 61 molds. At the same time, a matrix σq is erected, and a runner αD is formed downward from the upper surface of the matrix αQ, and a runner αD is bent at the upper part of the lower surface into the gap space between the matrix curve and the core mold (9). Using the original mold (7) with a sprue (to), the lower sprue method (moguri weir) is used, and high temperature hot metal is injected into the gap O2 from the sprue 03 provided at the bottom of the mother mold 00, and the steel is heated. The mold for the lump is cast. In this case, in order to form the mold of the present invention, it is necessary to apply a graphitization accelerator to the lower outer peripheral surface of the core mold (9), that is, the part where tone sheets are likely to occur, when forming the coating mold of the core mold (9). For example, the graphitization promoting mold opening 4 is formed by applying a mold coating agent containing ferrosilicon powder of 100 meshes or less mixed in a certain proportion.

Accordingly, when the hot metal solidifies, the cementite in the pearlite ground is decomposed to generate graphite and fetuite, thereby forming the inner layer (6) of the mold of the present invention. The binder for the coating agent may be either inorganic (eg, bentonite) or organic (eg, phenol resin).

The above is a case where the inner layer (6) is a cast iron mold made of ferrite, but the present invention is not limited to this, and the inner layer (6) is the outer layer (
It may also be an iron oxide layer integrally formed on the outer layer (5) by the oxidation reaction of 5). This iron oxide layer can be formed by blowing air to the inner surface at an inner surface temperature of approximately 700°C during the cooling process of the product (mold for steel ingot) after casting, or by a so-called corrosion method after cooling the completed pot. Formable.

As described above, in the mold of the present invention, at least in the lower part of the cast iron mold for shoulder lumps where tone sheets are likely to occur, the inner layer has a lower yield point at 0.2 to 1 degree lower than the inner surface of the mold that comes into contact with molten steel. It is made of iron-based material, and the outer layer is made of cast iron material in which graphite is uniformly dispersed and the base is pearlite, and the inner layer and outer periphery are metallurgically integrated, aiming to improve the quality of steel ingots in recent years. When punching out a steel ingot produced under the following conditions, the force acting diagonally and downward from the steel ingot to the mold will not reach the outer layer of the mold due to peeling of the inner layer of the mold, preventing tone sheets. Therefore, the life of the mold can be improved.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of tone sheet generation, Fig. 2 is a perspective view of the mold for generating tone sheet as seen from below, Fig. 3 is an explanatory diagram of the force acting on the mold from the steel ingot, and Fig. 4 is the invention of the present invention. Figures 5 to 8 are microscopic photographs (
xlooo), FIGS. 5 and 6 are micrographs showing the structure of the outer layer and inner layer of the cast 2N of the present invention, respectively, FIGS. 7 and 8 are microphotographs showing the structure of a conventional claw, and FIGS. 9
The figure shows a sectional view of a mold for manufacturing a mold according to the invention. (1)...mold, (2)...steel ingot, (3)...defective part, (4)...welded part, (5)...outer layer, (6)
... Inner layer, (7) ... Original mold, +81 ... Lower mold,
(91...core mold, Ql...matrix, mouth 4...graphitization promoting coating mold. Patent applicant: Kubota Iron Works Co., Ltd. Figure 5 Figure 7 Figure 6 Figure e

Claims (1)

[Claims] L: At least in the lower part of a cast iron mold for steel ingots where tone sheets are likely to occur, from the inner surface of the mold that comes into contact with molten steel) 0
．． The inner layer from 2 to 1 is made of iron-based material with a low yield point, and the outer layer is made of cast iron material in which graphite is uniformly dispersed and the base is pearlite, and the inner layer and outer layer are metallurgically integrated. A double-layer structure cast iron mold for steel ingots. 2. The double-layer cast iron mold for a steel ingot according to claim 1, wherein the iron-based material with a low yield point is a cast iron material in which graphite is uniformly dispersed and the base is ferrite. 8. The two-layer structure cast iron mold for steel ingots according to claim 1, wherein the iron-based material with a low yield point is an iron oxide material.