JPS5920418B2 - Manufacturing method of high chromium roll with a cavity in the core - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When manufacturing a composite roll in which the outer layer is made of a high chromium material, the core material is made of ductile cast iron, and a heater insertion hole for crown control is provided in the center of the roll, the present invention provides a method for forming a cast iron in the outer layer. The present invention relates to a novel manufacturing method that can prevent the toughness of the core material from being inhibited by Cr diffusion from the outer layer and ensure the toughness of the roll core in which heater insertion holes are provided.

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.

However, one of the composite rolls whose outer layer is made of high chromium material
As a seed, 40 mm in the center of the roll as shown in Figure 1.
There is a work roll for hot strip mills that has holes (cavities) about φ in diameter.

This work roll has a heater inserted into its hole.
During use, the roll is heated and the roll body diameter is changed partially or depending on the time of use, thereby controlling the so-called roll crown.

It is equipped with a function to control the thickness of rolled coils, etc.

In the case of rolls with such holes (cavities) in the core, the strength of the core material is particularly required, and it is recommended to use ductile cast iron, which has particularly good graphitization, as the core material. is necessary.

In other words, if the core has a cavity, a strong tangential stress, which is the sum of residual stress, thermal stress, and rolling stress during use, acts on the rim of the core, and if the strength of the core is insufficient, , the roll will break in the longitudinal direction.

For example, when used as a pre-work roll for hot strip mill finishing.

The stresses acting on the hole edge are: Residual stress: 9 to 10 kg Am2 Thermal stress: 5 to 6 kg Arn2 Stress due to rolling pressure: 7 to 8 kg/Wtm2 Total: 21 to 24 k
The strength of the core material is calculated as g/-.

A tensile strength of 40 kgArLM2 or more is required.

Therefore, in a composite roll having this type of cavity, high-grade cast iron or ductile cast iron containing many carbides cannot be used as the core material.

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 ductile cast iron, centrifugal force casting is used. If the core material molten metal is cast into the outer layer after forming the outer layer, a part of the inner surface of the outer layer with a high Cr content will be remelted, resulting in a problem that the core material will have a high Cr content after casting. .

In other words, as the Cr content of the ductile cast iron core material increases, graphitization is inhibited and the structure tends to have a large amount of carbide, and the structure with a large amount of carbide becomes hard and its toughness decreases. This creates an inconvenience that defeats the purpose of this type of composite roll, which uses ductile cast iron to provide toughness to the core material.

In view of the above-mentioned problems, the present invention has been developed by centrifugal casting to produce a composite roll having a cavity in the core where the outer layer is made of high chromium material and the core material is made of strong ductile cast iron.
This is an attempt to prevent the deterioration of toughness due to increased content by inoculation.

The manufacturing method of the present invention is characterized by the fact that the outer layer is made of a high chromium material containing 13 to 27% Cr, the core material is made of ductile cast iron, and the roll core is made of ductile cast iron. In the manufacturing method of a composite roll in which a heater insertion hole is provided for crown control in the outer layer, first the outer layer is formed by centrifugal casting, and then when the core material molten metal is cast into the outer layer, Fe- is added to the core material molten metal. Si inoculating agent such as 8i
The method is to add 0.1 to 1.0% in quantity and cast, and then to drill the heater insertion hole.

To explain the present invention in detail below, FIG. 1 shows a composite roll having a hollow core to be manufactured by the method of the present invention, the outer layer 1 of which is made of a high chromium material having the above composition, while the core material 2 is made of a graphitized material. It is made of good quality ductile cast iron, and has a heater insertion hole (cavity) 2 in the direction of its center axis.

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, I will explain the conventional core casting method. In the case of the outer layer 1 which is cast by horizontal centrifugal force, as shown in Fig. 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 3 for casting the core and neck parts of the composite roll in the outer layer 1, and the core material is poured from the upper end pot 8. It is customary to cast the core material 2 within the outer layer 1 by injecting molten metal.

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 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, the casting thickness of outer layer 1 is 100+o+. When the casting weight is 3 tons, the amount of erosion on the inner surface of the outer layer is about 15 tons, so the amount of diffusion and mixing of the outer layer material is about 400 kg.
The amount of Cr is 13 to 27% of that amount.

On the other hand, the casting weight of the ductile cast iron of core material 2 is 6 tons,
If the Cr content in the molten metal is 0.1%, the Cr content in the core material 2 after casting is 0.97 to 1.90.
%.

If the Cr content of the ductile cast iron 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 casting method has a problem in that the ductile cast iron of the core 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, in this method, an appropriate amount of inoculants such as Fe-8i and Ca-8i are added to the molten core material, and this inoculation effect promotes graphitization of the cast iron material forming the core material 2, ensuring its toughness. This is what we aim to do.

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

A centrifugal force casting mold 4 with an outer layer 1 inside, a lower mold 6° and an upper mold 7
As a result, a top-pouring vertical mold 9 similar to that shown in FIG. Molten core material is poured from a ladle 12 or the like into a casting mold 9 in which a predetermined casting cavity is formed by sand molds 10 and 11 set therein through a casting pot 8 placed on the upper mold γ. is injected, and at that 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.

Once the composite roll material made of high chromium material for the outer layer and ductile cast iron for the core material is completed in this way, it is subjected to strain relief heat treatment and rough machining. The insertion hole 2 is bored by processing means, and the desired composite high chromium loam having a cavity in the core is manufactured.

According to the method of the present invention as described above, the outer layer 1 is made of Cr13-2
In a composite roll using a high chromium material containing 7% and ductile cast iron as the core material 2, even if the Cr content of the ductile cast iron forming the core material 2 increases due to Cr diffusion mixing from the outer layer 1, its graphitization will not occur. This makes it possible to obtain a structure with less carbide and ensure the targeted toughness of the core material 2.

In contrast, in the case of the conventional example, the molten metal composition of ductile cast iron is
0.2% or less (Cr amount decreased), after graphite nodularization treatment,
Even if inoculation with Si content of 0.1 to 0.5% is performed using Fe-8i or the like in a ladle, the inoculation effect will not be sufficient due to the time until casting and the fading phenomenon during the period from casting to solidification. Graphitization effect could not be obtained.

To explain the amount of inoculant 14 added to the core material molten metal by this method, the Cr content of the ductile cast iron forming the core material 2 may increase to 0.9 to 2.0%, and this In such cases, the amount of inoculation is 0.1% Si.
The above is required.

However, when the amount of inoculation exceeds 1.0% Si, the amount of molten metal slag in 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. ,0
．． The effective range is 1% to 1.0%.

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 method, the core material molten metal whose Cr content is increased by Cr diffusion mixing from the outer layer 1 is properly inoculated at the time of casting, so that even if the Cr content 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 important to do so.

Now, to explain once again the outer layer material and core material of the composite roll that Kempo is targeting, the reason why the high chromium material forming the outer layer 1 is specified as containing (r13-27%) is as follows.
As an outer layer material for rolling rolls.

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, cast steel other than ductile cast iron can be used as the core material 2 as long as it has 1 toughness, but in this case, the Cr content is about 0.9 to 1.5%. Even if it increases, it will not have a big effect on the toughness, and in the end it will not match the intended purpose of the application.

As explained in detail above, according to the present invention, the outer layer is made of Cr.
A high chromium material containing 13 to 27%, and a core material made of ductile cast iron.When manufacturing a high chromium roll with a hollow core, the core material is cast into an outer layer formed by a centrifugal casting method. Proper inoculation of the core material molten metal during casting can prevent the toughness from being inhibited by Cr diffusion from the roll core, thereby improving the toughness of the roll core including the roll neck. A significant improvement effect can be obtained.

Therefore, according to the present invention, a composite roll for rolling with increased accident resistance and a long life is provided in a high chromium roll having a cavity of this type, which requires particularly strong toughness due to the opening of a heater insertion hole. It is something to do.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view illustrating a composite roll with a cavity in the core, Figure 2 is a cross-sectional view illustrating the centrifugal casting method for forming the outer layer of the composite roll, and Figure 3 is a conventional core casting method. FIG. 4 is a sectional view illustrating the core casting method according to the present invention. 1... Outer layer, 2... Core material, 2'... Heater insertion hole, 4... Centrifugal force casting mold, 6... Lower mold, 7...
Upper mold, 8-... Sekibachi for casting, 9... Vertical mold, 12
... Ladle, 13... Hopper, 14... Inoculant.

Claims (1)

[Claims] 1. In a composite roll manufacturing method in which the outer layer is made of a high chromium material containing 13 to 27% Cr, the core material is made of ductile cast iron, and a heater insertion hole for crown control is provided in the center of the roll, the outer layer is first After forming the outer layer by centrifugal casting, when casting the core molten metal into the outer layer, an inoculant such as FeSi is added to the core molten metal in an Si amount of o, i to 1.
1. A method for producing a high chromium roll having a cavity in the core, the method comprising casting with the addition of 0.0% and then drilling the heater insertion hole.