JPS5920417B2 - Manufacturing method of high chromium roll with strong core material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims at preventing the toughness of the core material cast into the outer layer from being inhibited by Cr diffusion from the outer layer when manufacturing a rolling composite roll in which the outer layer is made of a high chromium material. The present invention relates to the provision of a new manufacturing method that prevents.

Composite rolls whose outer layers are made of high chromium material are used in hot strip mills, cold strip mills, and other rolls for iron finishing.

The high chromium material used as the outer layer material of composite rolls generally has the following chemical composition (wt%), and due to its high Cr content, it has excellent wear resistance and roughness resistance. Moreover, it is characterized by high hardness and strength.

On the other hand, the core material of the above composite roll is cast steel, high-grade cast iron,
Alternatively, ductile cast iron is used, but cast iron is often more desirable from the viewpoint of reducing residual stress and thermal stress during use, as well as from the viewpoint of weldability with the outer layer during manufacturing. Therefore, the above cast iron is used as the core material. The use of wood is customary.

By the way, when manufacturing composite rolls, centrifugal force casting is mainly adopted, but when manufacturing a composite roll such as the one described above in which the outer layer is made of high chromium material and the core material is made of cast iron, centrifugal force casting is used to form the outer layer. If the core material molten metal is cast into this outer layer after forming, a part of the inner surface of the outer layer with a high Cr content will be remelted, resulting in a high Cr content in the core material after casting. .

In other words, in general, as the Cr content of cast iron increases, graphitization is inhibited and the structure tends to have a large amount of carbide.A structure with a large amount of carbide becomes hard and its toughness decreases, and as a result, the core material deteriorates. This results in the disadvantage that the original purpose of the composite roll, which is to provide toughness to the roll, is lost.

In view of the above problems, the present invention inoculates the deterioration of toughness due to an increase in the Cr content of the core material when manufacturing a composite roll using centrifugal force casting, in which the outer layer is made of a high chromium material and the core material is made of a strong cast iron material. What is the feature of the manufacturing method of the present invention in achieving such technical problems?

The outer layer is formed of a high chromium material containing (R13-27%),
In a method for manufacturing a composite roll in which the core material is made of ductile cast iron or high-grade cast iron, the outer layer is first formed by centrifugal casting, and then when the core material molten metal is cast into the outer layer, Fe-8i is added to the core material molten metal. The point is to add an inoculant such as 0.1 to 1.0% Si.

To explain the present invention in detail below, FIG. 1 shows a composite roll to be manufactured by the method of the present invention, and its outer layer 1
is a high chromium material having the above composition, while the core material 2 is made of high grade cast iron or ductile cast iron.

This composite roll is first manufactured by centrifugal casting.
Generally, a horizontal centrifugal casting method as shown in Fig. 2 is used to cast the seeds from a ladle into a centrifugal casting mold (mold) 4 having sand mold parts 3 on the inner surfaces of both ends. It is customary to form the outer layer 1 by casting the outer layer molten metal through a pot 5 or the like.

Of course, when casting the outer layer 1, other inclined molds may be used. It is also possible to apply a vertical centrifugal casting method.

As described above, the core material molten metal is cast in the second step into the outer layer 1 formed by the centrifugal casting method, thereby casting a composite roll in which the outer layer 1 and the core material 2 are welded together. It is.

First, let me explain about the conventional core casting method.In the case of the outer layer 1 which is cast by horizontal centrifugal force, as shown in Fig. 3, after the outer layer 1 has solidified, it remains inside. A centrifugal force casting mold 4 and a separately prepared lower mold 6
．． The upper mold 7 and the casting pot 8 constitute a top-pouring vertical mold 9 for casting the core and neck of the composite roll in the outer layer 1, and the core material molten metal is poured from the upper end pot 8. It is customary to cast the core material 2 within the outer layer 1 by injecting it.

In addition, the reason why the lower mold 6 and the upper mold 7 are connected above and below the centrifugal casting mold 4 in FIG. 3 is because the roll length of the composite roll to be manufactured is longer than the mold 4. Therefore, if the mold 4 is sufficiently long and the sand mold parts 3, 3 set on the inner surfaces of both ends thereof are extended to form a casting cavity for the roll neck part, the use of the lower mold 6 and the upper mold 7 becomes unnecessary. In this case, the centrifugal force casting mold 4 can be erected after casting the outer layer, and the molten core material can be poured from the upper opening.

However, according to such a conventional core casting method, the outer layer 1
The molten core material poured into the inner layer remelts a part of the inner surface of the outer layer 1, and as a result, the outer layer 1 and the core material 2 are integrated by welding. As a result, Cr contained in the outer layer 1 is diffused and mixed as the inner surface of the outer layer is eroded.

For example, if the casting thickness of outer layer 1 is -00 mm and the casting weight is 3 tons, the amount of erosion on the inner surface of the outer layer is 15 m.
The amount of diffusion and mixing of the outer layer material is approximately 400k.
g, and the Cr amount is 13 to 27 g.

On the other hand, the casting weight of core material 2 is 6 tons, and the Cr content of the molten metal is 6 tons.
If the content is 0.1φ, the Cr content of the core material 2 after casting will be 0.97 to 1.90%.

If the Cr content of the cast iron material forming the core material 2 increases in this way, its toughness, particularly its toughness, will be significantly impaired.

In the above explanation, the case where the outer layer 1 is formed by the horizontal centrifugal force casting method is described, but when the outer layer 1 is formed by other inclined or vertical centrifugal force casting methods, the rotation after the outer layer is formed may be changed. A method is adopted in which the molten core material is continuously cast into the outer layer 1 without stopping.

However, even in this case, the inner surface of the outer layer is eroded and damaged, resulting in a high chromium content in the arrow tension core material 2.

As described above, the conventional core material casting method has a problem in that the core material 2 inevitably becomes high in chromium.

Now, to explain the present invention for solving such problems, in the manufacturing method of the present invention, first, when forming the outer layer 1 of the composite roll, the conventional centrifugal casting method (horizontal casting method) described above is used. Of course, this depends on the type (inclined or vertical).

After solidification of the outer layer, the molten core material is poured into the outer layer 1 and the roll core including the neck portion is cast in the same manner as in the conventional method shown in Fig. 3. At this time, Fe-3i is used in the core molten metal in the water droplet.

An appropriate amount of an inoculant such as Ca-8i is added, and the inoculating effect promotes graphitization of the cast iron material forming the core material 2, thereby ensuring its toughness.

That is, when pouring the core material molten metal, as shown in FIG.

A centrifugal casting mold 4 containing an outer layer 1, a lower mold 6, and an upper mold 7
As a result, a top-pouring vertical mold 9 similar to that shown in FIG. Sand molds 10. A molten core material is poured from a ladle 12 or the like into the mold 9 in which a predetermined casting cavity is formed by the mold 9 through the casting pot 8 placed on the upper mold 7.
At this time, an inoculant 14 is continuously added to the molten core material in the small pot 8 from a hopper 13 provided above the small pot 8.

According to the method of the present invention as described above, the outer layer 1 is made of C413-2
In a composite roll in which the core material 2 is made of high-grade cast iron or ductile cast iron containing a high chromium material containing 7%, even if the Cr content of the cast iron material forming the core material 2 increases due to Cr diffusion mixing from the outer layer 1, Graphitization can be promoted, a structure with less carbide can be obtained, and the targeted toughness of the core material 2 can be ensured.

On the other hand, in the case of the conventional example, for example, when ductile cast iron is used as the core material 2, the molten metal composition is C3.6, Si2.5% (increased Si content), CrO
, 2% or less (decreased Cr content), and after graphite spheroidization treatment, even if inoculation with Si content of 0.1 to 0.5 with Fe-8i etc. is performed in a ladle, the casting time and Due to the fading phenomenon after casting until solidification, sufficient inoculation effect, that is, graphitization effect could not be obtained.

In addition, when using high-grade cast iron, it is generally C3.0 to 3.
Its normal composition is 6% SiO, 9~1.5%, and 0.2~0.8% Cr, but even in this case, the amount of Cr is 0.2%.
In addition to suppressing the amount of Si to 1.5 to promote graphitization,
Measures have been taken to increase the content to ~2.0%, but there is a limit to its graphitization.

To explain the amount of inoculant 14 added to the core molten metal due to its nature, in the case of ductile cast iron, the Cr
The amount of Si may increase to 0.9 to 2.0%, and in such cases, the amount of Si to be inoculated must be 0.1% or more.

However, when the amount of inoculation exceeds i,o% in terms of Si amount, the amount of dissolved slag of the inoculant increases, and foreign matter tends to be present at the boundary between the multilayer and the core material, making it unsuitable for manufacturing composite rolls. Become.

The amount of this inoculant added is the same even in the case of high-grade cast iron <0.1
~1.0% is an effective and appropriate range.

When adding the inoculant 14, it is important to continuously add it at a constant rate so that it is added uniformly over the entire molten core material to be cast.

In addition, in this case, proper inoculation is applied to the core material molten metal in which the amount of Cr is increased by diffusion and mixing of Cr from the outer layer 1 at the time of casting, so that even if the amount of Cr increases, graphitization of the core material 2 is promoted.
Although the toughness is ensured, from the viewpoint of improving the toughness of the core material 2 as much as possible, the Cr content of the core material molten metal itself to be cast is kept as small as possible (approximately 0.2% or less).
It is necessary to do so.

To explain once again the outer layer material and core material of the composite roll that Kempo targets, the reason why the high chromium material forming the outer layer 1 is specified as containing Cr13-27 is that the rolling roll outer layer As a material, materials in this range are becoming common as they have both wear resistance and roughness resistance.
Further, when the amount is below this range, the amount of Cr diffused into the core material 2 is small, and the influence on the toughness of the core material 2 is not as problematic as the left.

In addition to the above-mentioned high-grade cast iron and ductile cast iron, cast steel materials can also be used as the core material 2 as long as they have toughness, but in this case, the Cr content is 0.9 to 1.
Even if it increases to about 5%, it will not have a significant effect on toughness, and in the end it will not match the intended purpose of the application.

Next, examples of the present invention will be described along with comparative examples.

Using the molten metal with the chemical composition shown in Table 1 below, the conventional method shown in Fig. 3 and the original property shown in Fig.
0φX1422J! ! A high chromium roll for a hot strip mill finished front work roll with an outer layer casting thickness of 90 mrn (casting weight 6200 kg) was manufactured.

Here, in the conventional method, after the core material ductile cast iron is treated with Mg,
Inoculation was performed in a ladle by adding Fe-8i in an Si amount of 0.5%, and the Si amount after inoculation was the above-mentioned 2.31%.

However, in this case, 15 minutes passed from the time of inoculation in the ladle to the time of casting.

On the other hand, in the case of the method of the present invention, the amount of O8i in the core molten metal in the ladle was 1.99% as mentioned above, but by adding it to the molten metal in the pouring pot as shown in Figure 4, Fe-8i to Si
0.5% in amount, the amount of Si is 1.99% + 0.5
%-2.49% (calculated value).

However, in reality, the yield of Fe-8i is not 100%, so it is 2.49% or less.

A test piece was taken from the center of the body of the roll obtained by both methods and subjected to analysis and measurement of mechanical properties, and the results shown in Table 2 were obtained.

According to the above table, 1. In the method of the present invention, in the roll core.

Although it contains a high Cr content of 0.9% or more, it is confirmed that its toughness is significantly improved (particularly, the strength is 40 kgz4+'' or more).

The microscopic structure of the above customer test piece is shown in Figs. 5 and 6, and in the case of this method shown in Fig. 6, it is recognized that the target structure with less carbide is obtained. The inoculation effect of this method can also be confirmed from the top of the tissue.

As explained in detail above, according to the present invention, the outer layer is made of Cr.
When manufacturing high chromium materials containing 13 to 27 parts, high chromium loams in which the core material is made of high-grade cast iron or ductile cast iron,
It is possible to prevent the toughness of the core material cast into the outer layer formed by the centrifugal casting method from being inhibited by Cr diffusion from the outer layer by properly inoculating the molten core material during casting. This has the effect of significantly improving the toughness of the roll core including the roll neck.

Therefore, according to the present invention, a rolling composite roll with a long life and excellent accident resistance during use is provided.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view explaining the composite roll, Figure 2 is a cross-sectional view explaining the centrifugal casting method for forming the outer layer of the composite roll, and Figure 3 is a cross-sectional diagram explaining the conventional core casting method. , FIG. 4 is a cross-sectional view illustrating the core casting method according to the present invention, and FIGS. 5 and 6 are micrographs showing the structure of the roll core in comparison, and FIG. 5 is a conventional example, FIG. 6 shows an example of the invention. DESCRIPTION OF SYMBOLS 1... Outer layer, 2... Core material, 4... Centrifugal casting mold, 6... Lower mold, 7-... Upper mold, 8... Casting pot, 9... Vertical mold, 12... Ladle, 13... Hopper, 14... Inoculant.

Claims (1)

[Claims] 1 In a method for manufacturing a composite roll in which the outer layer is formed of a high chromium material containing 13 to 27% Cr and the core material is formed of ductile cast iron or high-grade cast iron, the outer layer is first formed by centrifugal casting, and then the inside of the outer layer is formed by centrifugal casting. When pouring the molten core material into the molten core material, add an inoculant such as Fe, Si, etc. to the molten core material in an Si amount of 0.1 to 1.0.
A manufacturing method for high-chromium rolls with a strong core material that emphasizes adding %.