JPS5928620B2 - Hot rolled roll material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the composition of rolls used for hot rolling of metals, and is particularly suitable for rolls that require seizure resistance and wear resistance.

In particular, rolls for reducing mills, which reduce the outer diameter by hot rolling seamless steel pipes that have been perforated by piercers, plug mills, reelers, etc., are used to reduce the outer diameter. Because of the large relative slippage between the roll and the material, it not only causes wear of the roll, but also a seizure phenomenon, which causes scratches on the surface of the product, which is becoming a serious problem.

Conventional reducer roll (bald) Pre-tiled roll (around 3.5% C, no alloy addition) (b) Low alloy grain roll (around 3.2% C, low alloy,
graphite precipitation) is commonly used.

However, in terms of wear resistance, there are generally no problems except for roughness due to the graphite part missing in (b), but due to the large slippage caused by hot conditions, seizure occurs on the upper part of the caliber 1, as shown in Figure 1. 2 is generated and gradually increases in the circumferential direction and continues in a circumferential manner, which causes a flow to occur on the outer surface of the product pipe, resulting in short roll usage time and roll life.

As a result of various studies regarding the seizure phenomenon, which is the most important factor determining roll usage time and roll life, the inventors have obtained the following knowledge.

That is, the seizing phenomenon of the reducer roll occurs due to the following two causes.

(A) Rolled material adheres to pits, cracks, graphite, carbide chips, etc. that occur on the roll surface.
Seizure (B) The rolled material adheres to the Maru-IJ tux and seizes.

Therefore, when attempts were made to reduce carbides as a countermeasure for (A), the seizure phenomenon could not be prevented, and wear increased, and the roll usage time was shortened on the contrary.

On the other hand, for (B), when we tried to increase the amount of carbide, seizure occurred due to lack of carbide (above A), and it was not possible to meet the conflicting demands of the two, and there was no suitable material. Ta.

In addition to the above-mentioned low-alloy grain or blenched roll materials, roll materials containing special carbides have recently been used for hot finishing rolling, such as high chromium rolls (representative examples are shown in Table 1 Comparative material (■)). C210~2.5% Or.

Publicly known documents include JP-A-53-76119 and Ir.
on and SteelEngineer 1975
0ctober 69 pages, etc.) are used.

Therefore, an attempt was made to use this high chromium material, but the result was that seizure could not be prevented and the wear resistance was also poor, making it unsuitable.

In addition, high carbon, high chromium materials similar to those of the present invention are mainly used as wear-resistant mechanical parts for construction machinery (for example, 2.50 to 4.50% C2
5-15Cr and other Mo.

"Wear-resistant white cast iron" with additions of W, V, Ni, Co, etc....Special Publication No. 42-23706 Table 1 Comparative Example V
>, No. 51-29493, No. 53-17525.

However, these are used in cold conditions and are intended only for wear resistance, and there is no need to consider seizure resistance or roughening resistance, and heat check resistance is not required.

Further, there is no particular need for compressive strength, and a very simple performance is sufficient compared to the various performances required of hot rolling rolls.

On the other hand, the material of the present invention is used under hot conditions where seizure is likely to occur, high surface pressure, and large slippage, without compromising wear resistance, which is not necessarily compatible with wear resistance. It improves seizure resistance and also fully satisfies the requirements for surface roughness resistance and heat crank resistance that are naturally required for hot rolling rolls.

Therefore, although the conventional "wear-resistant white cast iron" material used mainly for construction machinery is similar to the present invention in terms of composition, it is therefore not suitable for hot rolling rolls, which have completely different usage conditions. It is difficult to predict whether the
Naturally, it is not possible to predict its effects and effects.

For these reasons, high chromium rolls with a carbon content exceeding 3.5% have never been used at all.

The present invention prevents the rolled material from seizing on the rolls without impairing wear resistance, extends the usage time of the rolls,
The purpose is to extend the life of the roll by reducing the number of grinding operations.

The gist of the anti-seizure measures is as follows.

(A)-1 Strengthen the matrix (increase hot hardness),
Improved seizure resistance.

-2 Prevent seizure by crystallizing a large amount of carbide with a composition completely different from that of the rolled material.

(B) As the amount of carbide increases, seizure will decrease, but on the other hand, the shape of the carbide should be improved because cracks are more likely to occur and carbide is more likely to chip or fall off, increasing secondary seizure.

That is, the present invention is characterized by crystallizing a large amount of eutectic carbide, which is most effective in preventing seizure, and by dividing the conventional plate-like or net-like carbide into a granular or block-like shape. It has characteristics.

Therefore, there is no composition table for high carbon and high chromium, a large amount of eutectic carbide with an area ratio of 35 to 60%, and special carbide in granular form are crystallized.

Furthermore, Mo, W, and V are added to form Or, Mo, W, and V.
The purpose is to prevent seizure by making it easier and more stable to crystallize special carbides such as.

In addition, Mo, abrasion resistance can be improved without impairing accident resistance.
W.

This is improved by using a hard carbide such as V.

To explain the present invention more specifically, the components are 0.3% by weight.
．． 5-4.5, SiO, 3-2.5, Mn0
．． 3~2゜Or 10~25%, the balance consisting of iron and impurities, and Mo≦10 W≦10 V
It consists of a component in which one or more of two or more of ≦5% are added alone or in combination, and a component in which Ni≦5% is added to each of the above components, and the amount of carbide is 35 to 60% in terms of area ratio. This is a cast iron roll that uses a high carbon, high chromium material subjected to crystallization at least in the contact area (outer layer) with the material to be rolled.

Here, at least means that the entire roll may be made of the above-mentioned material, or as shown in the examples below, the material of the present invention is used as the outer layer only in the contact area with the material to be rolled, and the inner layer is made of strong cast iron. The purpose is that it may be used as a composite roll using.

In other words, C, Or
, Mo 2 , W, and V are added in increased amounts, and in particular, it contains a large amount of carbon and chromium.

Its feature is that by making the structure high in carbon and chromium, a large amount of special carbide in the form of grains and blocks can be crystallized at 35 to 60% (area ratio), completely preventing seizure. By adding Mo, W, and V, a special carbide can be formed more easily and stably, and the hardness of the carbide can be increased.

Further, Ni can strengthen the matrix and increase the hardness to a desired level.

Next, the reasons for limiting each component will be described.

0: 3.5-4.5% To secure the necessary amount of carbide, which is the most important for preventing seizure, 3.
A content of 5% or more is required; if it exceeds 4.5%, there will be too much carbide, and furthermore, it will be difficult to form the carbide into a granular shape, resulting in poor crack resistance.

Si: 0.3-2.5% 0.3% or more is necessary to deoxidize the molten metal, and as it increases, it promotes the granulation of carbides, but if it exceeds 2.5%, graphite crystallizes or It begins to precipitate and becomes a cause of rough skin, making it unsuitable.

Mn D 0.3-2% 0.3% or more is necessary for desulfurization, and as it increases, the hardness of the matrix increases, but when it exceeds 2%, retained austenite increases and the matrix hardens. hardness decreases.

Cr2 10-25% The anti-seizure content is also an important element, and it combines with iron and carbon to form a special carbide (Fe-Or) 7C3, but 10% or more is required for stable crystallization. If it is less than 10%, the amount of carbide and granulation will be insufficient and the anti-seizure effect will be low.

Moreover, if it exceeds 25%, the shape of the carbide changes and
Accident resistance also deteriorates.

Mo: 10% or less Forms a special carbide together with Or, promoting granulation and stabilization.

Also, very hard Mo2C and double carbides are used for crystallization.

Furthermore, it dissolves in solid solution in the Mad IJ in proportion to the amount added, significantly improving hardenability and strengthening the matrix, improving seizure resistance and wear resistance.

However, the effect tends to be saturated when added in excess of 10%.
Moreover, it is unnecessary because it is expensive.

W: 10% or less It is added for the same purpose as Mo.

Since the atomic weight is about twice that of Mo, it is 1/1/1 of Mo in weight%.
/2 amount has the same effect.

Furthermore, when the present invention is applied to rolls, they are often manufactured substantially by centrifugal casting, but in this case, if it exceeds 5%, segregation will occur and a uniform structure cannot be obtained, so it is preferably 5%. % or less is better.

725% or less It is added for the same purpose as Mo and W.

It is an element that tends to cause segregation, and if it exceeds 5%, segregation becomes significant, so it should be kept at 5% or less.

Ni: 5% or less It is added to strengthen Mal-IJ lux, refine the structure, and increase hardness, but the effect is saturated even if it exceeds 5%, and if it increases further, retained austenite increases. Mal
- This is not preferable because it actually lowers the IJ Lux hardness.

The compositions of each component have been described above, but in order to control the amount and shape of carbides to a more preferable state, it is desirable to keep them within the following ranges.

1 First, Or+HMo+7W2i 0 to 25% These three elements have a carbide forming effect together and can be substituted for each other.

When the total amount is less than 10%, both the amount and shape of the special carbide are insufficient, and when it exceeds 25%, the special carbide becomes excessive, the shape becomes bad, and the accident resistance deteriorates.

Carbide content 2: 35 to 60% The relationship between free carbide content and seizure is shown in Table 2. If it is less than 35%, seizure will be observed and the effect will be small, and wear will increase, resulting in insufficient results.

If it exceeds 60%, it becomes too much and at the same time, it becomes difficult to control the shape and the crack resistance deteriorates.

Although the percentage of carbide amount in Diagram 2 is expressed as an area ratio, it is also approximately the same as a volume ratio.

Next, the present invention will be explained based on examples.

Examples 1 and 2 A reducer roll for seamless steel pipe with product dimensions (fi) of 380φ (body diameter) x 187φi (inner diameter) x 152 (full length) was cast using a centrifugal casting method with as-cast dimensions of 400φ x 160φi x 1400. Outer layer material: book After casting a composite roll made of the high carbon, high chromium cast iron inner layer material of the invention and two strong cast irons, a plurality of rolls were cut off (circularly sliced).

The ingredients and casting conditions are as follows.

Casting conditions: casting temperature 1350°C, heat treatment temperature 450°C, finished hardness Example I H371-72, Example 272-74 Carbide amount (area ratio) Example 140-45% Example 242-
45% The results of using this roll (number of rolling rolls/times) are as follows.

Roll of the present invention Example 1 Example 2 5900 6100 Conventional roll 3,000 The roll according to the present invention shows no seizure phenomenon, has slight wear, and can be rolled (used) for about twice as long as conventional rolls. became.

In addition, in Example 2, approximately 1% Ni was added only to the outer layer material components of Example 1 (other components were the same) to strengthen the matrix,
The hardness was improved, and the results were slightly better than in Example 1.

The microstructures of Examples 1 and 2 are shown in Figure 3A.

Shown as B (X'65).

Figure 2 shows the microstructure of the conventional material.

Examples 3 and 4 Although the effects of the materials of the present invention were fully recognized in Examples 1 and 2, Mo was added to stabilize the shape of the special carbide in the form of grains or blocks and to crystallize or precipitate it.

W and ■ were added and dissolved to cast a test piece.

The composition of the outer layer material is shown in Table 4 (the inner layer material is Example 1).
).

The microstructure of the roll material obtained as a result is as shown in Figure 3C (Example 3) and tD (Example 4), and the shape of the special carbide is well granulated, which is superior to that of Example 1゜2. The result can be changed.

The amounts of free carbides in Examples are as follows.

As described above, the high carbon, high chromium cast iron roll according to the present invention did not suffer from significant seizure and could be used for about twice as long as conventional rolls.

The example shows the case where it is applied to a reducer roll, but it is also effective not only for pipe manufacturing but also for hot finishing rolls for copper strips and hot rolling rolls for metals, which require seizure resistance. (Seizure resistance, abrasion resistance, roughness resistance) can be expected.

In addition, when manufacturing the roll, it may be an integral roll or a composite roll, and high-grade cast iron, spheroidal graphite cast iron, or other materials may be used as the inner layer material.

The casting method can be any known method such as centrifugal casting or conventional casting.

By using the roll of the present invention, great effects can be obtained not only in reducing the unit consumption of the roll, but also in reducing the number of times of grinding and rearrangement, and reducing mill stop time.

[Brief explanation of the drawing]

FIG. 1 is a perspective view illustrating the seizure phenomenon of a reducer roll, where 1 is a caliber and 2 is a seizure phenomenon. Figure 2 is a micrograph (65x) showing the microstructure of a conventional roll material, (a) t (b) t (c)
The targets are as follows (numbers correspond to Table-1)
. (a) Pre-chilled roll (1) 3.5%C (
b) Low alloy grain roll (II) 3.2%C,
2.5%Ni, 1%0r (C) High Cro-ru (IV') 3%C216%
Figure 3 is a microscopic photograph (65x magnification) showing the microstructure of the roll material of the present invention, and the objects are as follows. (A) Example 14%C213%0r (B) II 2 4%C213%Or, 1
%N1(C) // 3 4%C210%Or
, 5%Mo. 5%W (D) II 4 4%C210%Or, 3
%Mo. 2%W, 5%V, 3%Ni

Claims (1)

[Claims] 1 Component composition in weight%: C3.5 to 4.5%, Si0
, 3-2.5%, Mno, 3-2%, 0r10-2
5%, the balance being iron and impurities, and the crystallization ratio is such that the amount of carbide is 35 to 60% in terms of area ratio.A hot rolled roll material with excellent seizure resistance and wear resistance. 2 Component composition in weight%, C3.5-4.5%, Si0
．． 3-2.5%, Mno, 3-2%, Or 10-
25% Ni, 5% or less Ni, the balance is iron and impurities, and the crystallization ratio is such that the amount of carbide varies by area ratio from 35 to 60%.A hot rolled roll material with excellent seizure resistance and wear resistance. 3 Component composition in weight%, C3.5-4.5%, SiO
,3-2.5%, Mn 0.3-2%, 0r10-2
5%, and Mo 10% or less, W 10% or less, 75%
A hot rolled roll material having excellent seizure resistance and abrasion resistance, which is made of one or more of the following, the balance being iron and impurities, and the crystallization ratio is such that the amount of carbide is 35 to 60% in terms of area ratio. 4 Component composition in weight%, 03.5-4.5%, St0
, 3~2.5%, Mn 0.3~2%, Cr 10~
25%, Ni 5% or less, and Mo 10% or less, W1
Hot-tempered steel with excellent seizure resistance and wear resistance, consisting of one or more types of 0% or less, 75% or less, the balance being iron and impurities, and the crystallization ratio is such that the amount of carbide is 35 to 60% in area ratio. Rolled roll material.