JPS5810982B2 - High hardness chrome roll for cold rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a work roll for cold rolling, in which the outer shell is made of a high-hardness, high-chromium material that has particularly excellent wear resistance and accident resistance.
This invention relates to a high-hardness, high-chromium roll consisting of a composite roll whose inner shell is made of cast iron having high toughness.

As is well known, currently Hs8 rolls are used for cold rolling.
A forged steel hardened roll having a hardness of 5 to 100 is generally used, and the layer used in this type of rolling roll is generally required to have the following properties.

Wear Resistance It is naturally desirable that the amount of wear caused by rolling is small, and this is determined by the hardness and amount of carbide.

Therefore, in the case of cold rolling rolls, in order to obtain wear resistance, the hardness is as high as possible, and structural uniformity is effective for uniform wear.

Accident resistance Accident resistance in cold rolling is caused by abnormal grinding of the rolls due to accidents during rolling such as seizure and squeezing, which greatly affects the life of the rolls.

On the other hand, the roll as a whole is required to have sufficient toughness in its body and neck in order to withstand a large rolling load.

However, in the above-mentioned forged steel quench roll, in order to ensure high hardness, the tempering temperature after quenching is carried out at a low temperature of 150 to 200 degrees Celsius in the manufacturing process. This has the disadvantage that it generates abnormal heat and generates large tensile stress in this part due to the restraint of other parts, resulting in easy occurrence of cracks and spalling.Also, even if the thermal effect is slight, high hardness parts may burn out. There was a problem in that a softened part was produced when the material was returned, and it was easy to cause dents and scratches.

In order to solve the above-mentioned problems in cold rolling rolls, the present invention proposes a new composite roll in which the outer shell is made of a high-hardness, high-chromium material and the inner shell is made of a cast iron material, in place of the conventional forged steel hardened roll. The present invention provides a high-hardness chromium roll, and the present invention is characterized by a composite roll in which an outer shell and an inner shell are completely welded and integrated, in which the outer shell is made of C.
23, ~3.0%, Si0.4~1.0%, Ni1.5
~3.0%, Cr13~22%, Mo 1.5~3.5
%, Mn 0.5-1.5%, the remainder substantially consists of Fe, and has a hardness of Hs 80 or more, and the inner shell is C2,8-1.5%.
3.4%, Si 2.5-3.0%, Cr 2% or less, others Mn, Ni.

The total amount of one or more types of Mo is 2.5% or less, and the remainder is substantially composed of Fe.

The present invention will be explained in detail below.

As mentioned above, in the high hardness, high chromium roll of the present invention, the outer shell, which corresponds to its use layer, is formed of a high hardness, high chromium material that has the required wear resistance and accident resistance, while the inner shell is made of a tough and high chromium material. In order to compensate for the shortage, it is made of strong cast iron material.1. Moreover, it consists of a composite roll whose outer and inner shells are completely welded together.

First, the outer shell material of the roll of the present invention will be explained. The range of each component and the reason for its limitation are as follows.

C: 2.3 to 3.0%, Cr: 13 to 22%C content has a great influence on the shape and amount of carbide depending on the balance with Cr content, and is especially important for highly hard and uniform carbide. In order to obtain a bite (in the present invention, the target hardness of the outer shell is H
s 80 or more), Cr carbide area is 25
% or more, and for this the amount of C must be 2.3% or more.
% or more is required.

However, if the C content exceeds 3.0%, the carbide content will increase significantly and the hardness will further increase, but this will cause casting cracks and is therefore unsuitable.

Regarding the Cr content, the ratio of the amount of C to the amount of Cr is 1:5.
．． Unless it is 5 or more, fine and uniform Cr carbide cannot be obtained, and therefore the Cr content is required to be 13 to 22%.

If the Cr content is 22% or more, coarse Cr carbide will appear and the non-uniformity of the carbide will become significant, making it unsuitable.

Si: 0.4-1.0% Si is required at 0.4% or more to deoxidize molten iron, but if it is 1.0% or more, it contributes to an increase in hardness, but on the other hand, the material becomes brittle. The upper limit is set at 1.0%.

Ni: 1.5-3.0%, Mo: 1.5-3.
5% Ni is required to be 1.5% or more in order to obtain the target high hardness.

However, if the content exceeds 3.0%, a corresponding effect in increasing the hardness cannot be obtained, so the upper limit is set at 3.0%.

Also, as with Ni, 1.5% or more of Mo is required in order to obtain a high hardness of Hs80 or more.

However, if it exceeds 35%, it will not have much effect on the base structure and will enter the carbide, so from an economical point of view, the upper limit is set at 3.5%.

Mn: 0.5-1.5% Regarding Mn%, 0.5% or more is necessary for deoxidizing molten iron, and if it is 1.5% or more, like Si, it contributes to an increase in hardness, but on the other hand, it Since it becomes brittle, the upper limit is set to 1.
Specified at 5%.

The basic composition of the high hardness, high chromium material that forms the outer shell is the above-mentioned components, but if necessary, some other alloying elements may be included, and the remainder is impurities. It consists essentially of Fe except for.

Next, the inner shell material of the roll of the present invention will be explained. In the inner shell, components of the outer shell, especially Cr, partially diffuse and inhibit graphitization.
It is necessary to select the range of ingredients taking into consideration in advance that the material will be hard and brittle.

C: 2.8-3.4% If the C content is less than 2.8%, graphitization will be insufficient.1. The required toughness cannot be obtained, and on the other hand, if it exceeds 3.4%, too much graphite will be produced, resulting in a brittle material, although it depends on the balance with the amount of Si, which will be described later.

St: 2.5 to 3.0% The Si content has the effect of canceling out the influence of Cr diffusion from the outer shell, and is required to be 2.5% or more.

However, if it exceeds 3.0%, graphitization becomes coarse and the material becomes brittle.

As for the method of adding Si, for example, the Si content in the molten metal is adjusted to 2.5%, and then Fe-8 is added at the time of casting.
Even better results can be obtained if inoculation, such as adding 0.3 to 0.4% of i, is used in combination.

Cr: 2.0% or less (0.2% or less in molten metal) Cr in the inner shell
The content is preferably 2.0% or less, and as small as possible.

That is, according to the experimental results in which only the Cr content was gradually increased within the specific chemical composition range of the inner shell, Cr2.0%
It was found that the above method resulted in whitening of the inner shell and that sufficient toughness could not be obtained in the roll shaft core.

Therefore, it is necessary to limit the Cr content of the inner shell to 2.0% or less, but for this purpose, as mentioned above, the amount of Cr diffused from the outer shell must be taken into account in advance, and the C
It is necessary to limit the amount of r, and although it depends on the degree of diffusion, it is desirable that the Cr content in the inner shell molten metal is 0.2% or less, and as small as possible.

In addition to the above, the strong cast iron material forming the inner shell is Mn.

Contains 2.5% or less of one or more of Ni and Mo.

These elements are necessary to ensure the toughness of the inner shell, but if the total content exceeds 2.5%, the inner shell becomes too hard, resulting in poor toughness and is also economically disadvantageous.

The remainder consists essentially of Fe, excluding impurities.

To explain the manufacturing method of the roll of the present invention as described above, the manufacturing method of the composite roll generally includes hollow casting method,
Sliding gate method and centrifugal force casting method are used, but in the case of this roll, control of outer shell thickness,
In light of the problem of Cr diffusion into the inner shell, centrifugal casting is the easiest and most economical method to manage.

Therefore, when manufacturing the roll of the present invention as shown in the drawings by centrifugal force casting, an example is given. First, an outer shell 1 is formed on a mold that is coated with an appropriate coating on the inner surface and rotated on a centrifugal force casting machine. In order, C2, 3-3.0%, Si0,
5-1.0%, Ni1.5-3.0%, Cr13-22
%, Mo 1.5 to 3.5%, Mn 0.5 to 1.5%, and the remainder Fe, and the inner shell 2 is formed when the inner surface of the outer shell 1 is unsolidified or after solidification. C2,5
-34% Si, 2.5-3.0% Si, 0.2% Cr or less, and 2.5% or less of one or more of Mn, Ni, and Mo, and the balance is Fe. (In this case, it is not limited to centrifugal casting method)
As a result, the roll of the present invention in which the outer and inner shells are completely metallurgically integrated is manufactured.

In order to reduce the Cr content of the inner shell 2 to 2.0% or less after manufacturing, the amount of Cr in the molten inner shell is limited, and the proportion of the outer shell 1 that is partially dissolved by the molten inner shell is adjusted. For this purpose, the timing of casting the molten inner shell must be particularly selected.

A specific embodiment of the present invention will now be described, starting with its manufacturing process.

<Example> This example is an example in which the present invention is applied to a roll having a product body diameter of 590φ, a body length of 16701 mm, and a total length of 38001 mm.

Outer shell casting conditions The outer shell has a wall thickness of 95 mm (casting weight 2250 kg).
The high C and high Cr molten metal was centrifugally cast in a rotary mold at a casting temperature of 1400°C.

Inner shell casting conditions 25 minutes after the start of casting the outer shell, stop the rotation of the mold, and after confirming that the outer shell has completely solidified, stand the mold vertically and stop the rotation of the mold. 45 minutes later, casting temperature 13
Molten cast iron was poured from the top of the mold at 80°C and completely welded to the outer shell.

The composition of the molten metal before casting the outer shell and inner shell is as follows:
As shown in the table.

The results of ultrasonic testing and destructive testing of the body of the above-mentioned composite roll after machining confirmed that the outer shell and inner shell were completely welded and were structurally continuous. At the same time, the outer shell thickness is washed by the inner shell 6
It had decreased to 2 to 65 mm.

As the outer shell was washed, the Cr content in the inner shell, which was 0.05% when molten, was reduced to 1.62% in the center of the shell.
%, the upper neck area increased to 1.05%, and the lower neck area increased to 1.65%.

Further, as a result of performing a two-stage tempering treatment at 550° C. for 15 hours on the roll of this example, a shell hardness of 80 to 84 Hs was obtained.

Although the roll of this example contains about 1.0 to 2°0% Cr in the inner shell, its strength and toughness are still higher than that of ordinary cast iron material, as shown in Table 2 below. I understand that it belongs to the category of excellent ones.

As described above, in the high hardness, high chromium roll (composite roll) of the present invention in which the outer shell is made of a high hardness, high Cr material and the inner shell is made of a strong cast iron material, the outer shell has a high hardness of about Hv1400. Approximately 30% of chromium carbide is obtained in the structure, and the base structure already exhibits martensite and austenite in the as-cast state, but 5
By performing the tempering treatment at around 00°C, a tempered martensitic structure with high hardness can be obtained, and the outer shell exhibits sufficient wear resistance due to these high hardness carbide and matrix structures.

The outer shell exhibits almost no change in hardness throughout its thickness, and can be used under the same conditions from the initial diameter to the disposal diameter.

In addition, in the roll of the present invention, the tempering temperature is raised to a higher temperature of around 500°C compared to 150 to 200°C for forged steel quenched rolls, so it is difficult to prevent sudden temperature rises during abnormal rolling. It maintains stable hardness without being tempered, making it difficult to crack, and the residual stress is lower than that of hardened rolls, resulting in stable spalling resistance, and the outer shell has sufficient accident resistance. It is equipped with the following.

On the other hand, since the inner shell of the roll of the present invention is made of a cast iron material with high toughness, the roll as a whole has sufficient toughness.

Therefore, if the high hardness, high chromium roll of the present invention is used as a cold rolling pre-work roll in place of the conventional forged steel hardening roll, its performance and service life will be significantly improved.

[Brief explanation of the drawing]

The accompanying drawing is a sectional view showing an example of a composite roll.

Claims (1)

[Claims] 1 In a composite roll in which an outer shell and an inner shell are completely welded and integrated, the outer shell contains 3 to 3.0% C2, SiO,4
~1.0%, Ni 1.5-3.0%, Cr13-22
%, Mo 1.5-3.5%, Mn 0.5-1.5%
, the remainder substantially consists of Fe and has a hardness of Hs 80 or more, and the inner shell is composed of 8 to 3.4% C and 2.5 to 3.4% Si.
0%, Cr 2% or less, the total of one or more of Mn, Ni, and Mo is 2.5% or less, the remainder is substantially F
A high hardness, high chromium roll for cold rolling characterized by consisting of e.