JPS5920415B2 - Manufacturing method of high chromium roll with strong core material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention aims to reduce the Cr content of the core material cast into the outer layer and increase its toughness 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 novel manufacturing method.

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 this composite roll 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 the core material, a part of the inner surface of the outer layer having a high Cr content is remelted, resulting in a problem that the Cr content of the core material after casting becomes high.

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 has a lower toughness, and as a result, the core material becomes hard. 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 aims to prevent an increase in the Cr content of the core material as much as possible 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.
Therefore, the aim is to ensure its toughness, and the manufacturing method of the present invention is distinctive in achieving this technical objective.

In a method for manufacturing a composite roll in which the outer layer is formed of a high chromium material containing Cr13-27 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 inner layer is formed by centrifugal casting. A vertical casting mold for casting a roll core in the outer layer is constituted by a centrifugal casting mold having a casting hole, a lower mold having a casting hole, and an upper mold having a molten metal discharge port, and the vertical casting mold has a centrifugal force casting mold having The molten core material is continuously injected from the casting pipe, and the molten core material pushed up inside the mold is discharged from the molten metal outlet to replace the molten core material in the mold with the molten core material after pouring. After that, the molten metal for post-vaginal core injection material is solidified to reduce the amount of Cr in the roll core to 0.9 or less.

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, as shown in Fig. 2, a horizontal centrifugal casting method is used to cast the seeds from a ladle into a centrifugal casting mold (mold) 4, which has sand mold parts 3, 3 on the inner surface 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 type and vertical centrifugal force casting methods can also be applied.

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 portion of the composite roll in the outer layer 1. It is customary to cast the core material 2 within the outer layer 1 by injecting a core material molten metal.

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 of the mold 4 are extended to form a casting cavity for the roll neck part, the lower mold 6' and the upper mold 7' can be formed.
In this case, the centrifugal casting mold 4 can be stood up after the outer layer is cast, and the molten core material can be poured from the upper opening.

However, according to such a conventional core casting method.

The molten core material poured into the outer layer 1 re-melts 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. In this case, the 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 the outer layer 1 is 100 mm and the casting weight is 3 tons, the amount of erosion on the inner surface of the outer layer is 15r/1m.
The amount of diffusion and mixing of the outer layer material is approximately 400 kg.
The amount of Cr is 13 to 27 of them.

On the other hand, the casting weight of core material 2 is 6 tons, and the C of the molten metal is 6 tons.
If the r content is 0.1%, the Cr content of the core material 2 after casting is 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, firstly, in the manufacturing method of the present invention, when forming the outer layer 1 of the composite roll, the conventional centrifugal casting method (horizontal casting method) described above is used. After the outer layer solidifies, when the core material molten metal is cast into the outer layer 1 and the roll core including the neck portion is cast, as shown in FIG. A centrifugal force casting mold 4 that still contains a lower mold 6 that is equipped with a separately prepared casting shaft 10.
and an upper mold 7 having a molten metal outlet 11.

This constitutes a vertical mold 12 for bottom pouring.

The mold 12 for casting the roll core in the outer layer 1 will be explained with reference to FIG. 4. First, at the base of the mold 12, a pouring hole 13 is provided at a position higher than the casting amount of the composite roll. A casting pipe 10 communicates with the casting pipe 14 via the injection pipe 14.
A lower mold 6 having a side thereof is installed, and a centrifugal force casting mold 4 having an outer layer 1 therein is erected thereon.

And on top of this mold 4. An upper mold I having a molten metal outlet 11 on the side is placed, and the centrifugal casting mold 4
With the outer layer 1 and sand molds 3, 3 on the inner surface of, and sand molds 15, 16 set on the inner surfaces of the lower mold 6 and upper mold 7, respectively,
A mold 12 is constructed in which casting cavities for the roll core and roll neck are formed.

Note that below the molten metal discharge port 11, this discharge port 11
A receiver 17 for the molten metal overflowing therefrom is arranged as will be described later.

When pouring the core material molten metal into such a mold 12, the injection pipe 14. The core material molten metal is continuously injected into the mold 12 through the casting pipe 10, and even after the surface of the molten metal has been pushed up to the level of the molten metal outlet 11 of the upper mold 7, casting continues. And mold 12
The molten metal of the pre-poured core material inside is replaced with the molten metal of the post-poured core material, and the molten metal is allowed to overflow from the discharge port 11.

That is, in this method, the inner surface of the outer layer 1 is washed and the pre-poured core material molten metal with increased Cr content is sequentially overflowed from the discharge port 11,
The inside of the mold 12 is filled with the molten core material after the amount of Cr diffused from the outer layer 1 is small.

At this time, if the amount of Cr in the core molten metal overflowing from the discharge port 11 is analyzed and investigated in advance, it is possible to create a standard for the optimum amount of core material molten metal to be poured.

After completing the replacement of the required core material molten metal in this manner, the pouring from the secondary bowl 13 is stopped, the molten metal discharge port 11 of the upper mold 7 is closed by an appropriate means, and then the opening end of the upper mold 7 is closed. Casting is carried out at a predetermined casting height, and in this state the mold 12 is
After filling the inside, the molten core material is completely solidified.

In this way, cast iron with a low C4 content, that is, excellent toughness, is cast into the roll core and roll neck.

According to the method of the present invention as described above, the outer layer 1 is made of Cr13-2
In a composite roll in which the core material 2 is made of high-chromium material and the core material 2 is made of high-grade cast iron or ductile cast iron.

In particular, it is easy to suppress the Cr content of the cast iron material forming the core material 2 to 0.9 or less.

For example, when using ductile cast iron as the core material 2, C3, 0 to 3.6%, Si 1.8 to 2.5%,
A composition with CrO of 9% or less is suitable in terms of hardness and toughness, and if CrO is 9% or more, the steel becomes hard and the toughness decreases.

(In this case, there is a method of increasing the amount of Si to 25% or more to promote graphitization, but there is a limit to securing toughness).

Also, even when high-grade cast iron is used as the core material 2. C3,0～
3.6%, Si0.9-1,51%, CrO12-0.
The suitable composition is 8th column, and the Cr content is 0.9 to 1.
If it were to become as strong as 5, its toughness would be severely compromised.

(In this case, it is also possible to increase the amount of Si to 2.0 to 3.0% to promote graphitization.

To ensure toughness (it is desirable to suppress Cr to 0.9% or less).

That is, according to the single method, the Cr content of the cast iron material forming the core material 2 is reduced to 0.9%, which is particularly necessary to ensure its toughness.
or less, thereby sufficiently achieving the target toughness of the core material 2.

In addition, in this method, when the core material molten metal is poured as described above, the Cr content of the core material 2 is reduced by replacing the pre-poured molten metal with the post-poured molten metal.
From the viewpoint of keeping the Cr content of the core material to as low as possible, 0.9% or less, it is important to keep the Cr content of the core molten metal itself as small as possible (approximately 0.2% or less). be.

Once again, we will explain the outer layer material and core material of the composite roll that Mizutoshi is targeting. As a material.

Products in this range are common as they have both wear resistance and roughness resistance, and in cases below this range, the amount of Cr diffused into the core material 2 is small, and the toughness of the core material 2 is affected. This is because the impact on the population is not as much of a problem as it is on 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 big effect on toughness, and it will not match the purpose of application of Kempo after all.

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

Using molten metal with the chemical composition shown in Table 1 below,
By the conventional method shown in the figure and the present method shown in Fig. 4, the roll size is 6.
A high chromium roll of 50φ×14221mm and outer layer casting thickness of 90rILrA was manufactured.

Test pieces were taken from the center of the body of the rolls obtained by both methods and subjected to analysis and mechanical property measurements, and the results shown in Table 2 were obtained.

According to the above table, in the method of the present invention, 7) C
It is confirmed that the r content is suppressed to 0.9% or less and the toughness is significantly improved.

The microscopic structure of the father's specimen is shown in Figures 5 and 6, and in the case of Kenpo shown in Figure 6.

It is observed that the target structure with few carbides has been obtained.

5.Comparing the method of the present invention with the conventional method. Although a large amount of molten core material is required to be cast and the yield is reduced, this drawback is more than compensated for by the remarkable improvement in roll performance due to the strengthening of the core material.

As explained in detail above, according to the present invention, the outer layer is made of Cr.
When manufacturing high chromium rolls, the core material is made of high-grade cast iron or ductile cast iron.
It is possible to suppress the Cr content of the core material cast into the outer layer formed by the centrifugal casting method to 0.9% or less. The effect of significantly improving toughness can be obtained.

Therefore, according to the present invention, it is possible to provide a high-performance, long-life rolling composite roll that is unlikely to break or spall during use.

[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 force casting mold, 6... Lower mold, 7... Upper mold, 10... Seki for casting, 11... Molten metal Discharge port, 12... Bottom pouring vertical mold for casting the roll core in the outer layer.

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 (r) 13 to 27% 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 A vertical casting mold for casting a roll core in the outer layer is constituted by a centrifugal casting mold lining the outer layer, a lower mold having a casting hole, and an upper mold having a molten metal outlet, The molten core material is continuously injected into the same mold from the casting hole, and the molten core material pushed up inside the mold is discharged from the molten metal outlet, and the molten core material previously poured in the mold is subsequently poured. A method for manufacturing a high chromium roll having a strong core material, characterized by replacing the core material with a molten metal, and then solidifying the core material molten metal after the vagina to reduce the CrJt of the roll core to 0.9 or less.