JPH01127646A - Roll for hot rolling - Google Patents

Abstract

PURPOSE:To provide the title roll with wear resistance and seizure resistance endurable sufficiently under the conditions of high load rolling by specifying the compsn. at least of the outer layer of the roll and Cr/C in the components. CONSTITUTION:At least the outer layer of the roll for hot rolling is constituted of, by weight, 2.2-3.7% C, 0.4-3.5% Si, 0.5-1.5% Mn, <=0.08% P, <=0.08% S, >5.0-15.0% Ni, 2.2-13.0% Cr, >2.0-10.0% Mo, 0.02-2.5% Al and the balance Fe with inevitable impurities; and it satisfies 1.0-3.0% Cr/C. Total <=1.0% of one or more kinds among Nb, V, W, Zr and Ti are furthermore incorporated thereto at need. The outer layer is moreover formed into chilled alloy or grain alloy. By this method, the durability of finish work roll, etc., can be improved.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a hot rolling roll with excellent wear resistance and seizure resistance, suitable for use as a finishing work roll in hot rolling, for example. It is something.

(Conventional technology) In recent years, against the backdrop of the remarkable development of industrial technology, various materials with new characteristics have been developed, and at the same time, various rolled metal materials are being developed depending on their uses. things came into use. For this reason,
Rolls for rolling metallic materials are now required to have various strict characteristics depending on their purpose of use. Traditionally, various efforts have been made to improve the material, etc., but currently finishing work rolls for hot rolling of steel, which tend to be used under particularly harsh conditions, are using adamite materials and high-grade materials for the outer layer material. The mainstream is now made of wear-resistant tough cast iron such as chromium material or high-alloy grain material.

Note that among these roll materials, adamite materials are widely used as outer layer materials for work rolls in the first stage of finish rolling because they have a characteristic of being particularly strong. Also,
The high chromium material is a high hardness carbide CCr that exists in Mi loom.
5 Fe)ycs has excellent wear resistance.
In addition to high thermal conductivity due to the graphite present in the structure, the high-grade gold grain material also has the characteristics of excellent seizure resistance due to the lubricating action of the graphite itself. , efforts have been made to use it under conditions that take advantage of these characteristics.

On the other hand, recently, Nihard (product name: Structural Ni-
Cr chilled cast iron (4 types of component compositions are specified), the Si content of the well-known material is increased and graphite, which does not normally appear, is crystallized in the structure to improve thermal conductivity.
As a result, a rolling roll outer layer material with improved seizure resistance was proposed (Special Publication No. 61-16336, Japanese Patent Publication No. 61-1633,
-16415).

(Problems with the prior art) However, the above-mentioned adamite material has problems such as insufficient performance in terms of wear resistance and roughness resistance when the usage conditions become severe, and the high-chromium material The material has a lower thermal conductivity than other roll materials, so it has a noticeable lack of seizure resistance under severe usage conditions, and it also has the disadvantage of causing hangnail-like roughness on the entire surface. When the usage conditions become severe, the graphite in the structure of the elevated gold grain material acts adversely, causing wear and roughness originating from the graphite, which deteriorates the roughness and abrasion resistance. The problem was pointed out.

Furthermore, the aforementioned Special Publication No. 61-16336 and Special Publication No. 61-1
As a result of detailed examination through actual work, the roll outer layer material proposed as No. 6415 contained a large amount of Si to cause graphite crystallization in the structure, so the mechanical properties necessary for a roll material were significantly improved. In addition, when used under especially severe conditions, the graphite flakes off significantly, and we were forced to conclude that the abrasion resistance was not fully satisfactory.

Moreover, the roll outer layer material according to the above proposal has a Cr content of 5.
0 to 10.0% (hereinafter, "%" indicating the component ratio is "weight%"), which is very low compared to high chromium materials used for boat fishing, so even if M? C3 type high hardness carbide (CryCs+ F
egC3, etc.), even if they exist, it is only a small amount, and -I
It was also not possible to achieve the high-temperature, high-wear resistance that exists in n-type high-chromium materials.

As described above, all conventionally known roll materials have advantages and disadvantages. Therefore, it is particularly suitable for rolling under particularly harsh conditions such as "special steel rolling," 6-low temperature rolling, or "thin material rolling," that is, high-load rolling. At present, there has been a long-awaited roll material that has both superior wear resistance and seizure resistance.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to solve the above-mentioned problems pointed out in conventional hot rolling rolls, and also to solve problems that are becoming increasingly severe due to increases in high-load rolling. It is an object of the present invention to provide a hot rolling roll having both abrasion resistance and seizure resistance that are sufficiently satisfactory even under modern usage conditions.

(Means for Solving the Problem) In order to achieve the above object, the inventors of the present invention, in particular, It is effective to aim for the Based on the knowledge that quantity is the key, as a result of further intensive research, we obtained new knowledge as shown in the following (al or C1) and completed the present invention.

(Al friction coefficient decreases as the Cr/C ratio decreases. In other words, the seizure resistance improves as the Cr/C ratio decreases. However, if it is too small, problems will occur in terms of wear resistance. This tendency holds true regardless of the type of graphite in the roll Mi weave (chilled alloy, grain alloy).

) Addition of a large amount of Mo and Al exceeding the conventional level is effective in preventing flaking of graphite and carbides at high temperatures. In particular, although the benefits of graphite in the structure have been recognized in the past, the content has often been limited because a large amount of graphite can promote flaking. However, M.O.
If the high-temperature properties of the matrix, including its high-temperature softening resistance, are improved by adding a large amount of As a result, it is possible to contain a large amount of graphite, so that seizure resistance can be significantly increased without deterioration of other properties such as wear resistance. In this way, the improvement of the high-temperature properties of the base by adding a large amount of Mo makes these two properties compatible at a high level, and has a great effect on improving the properties of hot rolling rolls.

In addition, by adding a large amount of M, heat resistance is dramatically improved, and further improvements in wear resistance and seizure resistance can be expected.

In addition, since Al is a strong graphitization-promoting element along with Si, adding an appropriate amount may result in high S content that causes deterioration of mechanical properties.
It is possible to crystallize a large amount of graphite without having to process it.

(There is a range in the amount of C1 graphite crystallization where both wear resistance and seizure resistance are satisfactorily balanced.

Therefore, the present invention was developed based on such unique knowledge, and the gist thereof is that at least the outer layer contains, by weight, C: 2.2 to 3.7%, Si: 0.4 to 3.5%
, Mn: 0.5 to 1.5%, P: 0.08% or less, s: o, os% or less, Ni: more than 5.0% to 15.0%, Cr: 2.2 to 13.0 %, Ao:
More than 2.0% to 10.0%, 8Q: 0.02 to 2.
5%, balance: Fe and unavoidable impurities, and is a hot rolling roll characterized in that it is made of an alloy that satisfies Cr/C=(1.0-3.5).

The above alloys defined in the present invention can be broadly classified into chilled alloys and grain alloys depending on the presence or absence of graphite in the vA weave. Of course, both of them have excellent wear resistance and seizure resistance, but grain alloys in particular not only have much improved seizure resistance than chilled alloys, but also preferably contain The area ratio of the crystallized graphite phase is 1
．． By limiting the content to 0 to 4.0%, wear resistance and seizure resistance can be balanced even more favorably and both can be satisfied. On the other hand, chilled alloys are inferior to grain alloys in seizure resistance due to the fact that they do not crystallize graphite, but conversely, their wear resistance is further improved due to the large amount of carbides.

(Function) As described above, in the hot rolling roll according to the present invention, by regulating the Cr/C ratio of at least the outer layer material to 1 to 3.5, it is possible to achieve the contradictory properties of wear resistance and seizure resistance. It achieves both high-dimensional properties and also includes high temperature softening resistance by containing No over 2.0% to 10% and Al at a high ratio far exceeding the conventional level of 0.02 to 2.5%. We were able to dramatically improve various high-temperature properties and achieve remarkable high-temperature wear resistance.

When used as a chilled alloy, it is necessary to prevent the flaking of carbides present in large quantities.On the other hand, when used as a grain alloy, attention is paid to crystallized graphite, and the balance between the lubricating effect of graphite and the wear accelerating effect due to shedding is achieved. Taking this into consideration, by preferably setting the content area ratio to 1.0 to 4.0%, it is possible to realize a roll material for hot rolling that has both excellent wear resistance and seizure resistance.

Next, the reason for limiting the components of the outer layer material employed in the hot rolling roll of the present invention, and the reason for numerically limiting the Cr/C ratio and the amount of crystallized graphite in the structure as described above will be explained.

C: 2.2 to 3.7% The C component combines with Cr and Mo to form a high hardness carbide, and has the effect of ensuring properties such as hardness and abrasion resistance necessary for a roll material. , and Si, Ni, Al, which will be described later.
The graphitization-promoting element crystallizes graphite in the structure and has the effect of improving seizure resistance, but if the content is less than 2.2%, carbides are insufficient and sufficient hardness cannot be obtained. On the other hand, if the content exceeds 3.7%, the mechanical properties will deteriorate, such as increasing carbides and making the material brittle. It is set at 3.7%.

Si: 0.4-3.5% Si is an essential element for deoxidizing the molten metal and ensuring flowability, as well as for crystallizing graphite, but if it is less than 0.4%, the fluidity of the molten metal will be insufficient. In addition, it becomes difficult for graphite to crystallize.

On the other hand, if Si is added in excess of 3.5%, precipitation of carbides will decrease, making it impossible to secure the desired wear resistance.
The hardenability is inhibited, which tends to result in an incompletely hardened state, which leads to a decrease in base hardness, deterioration of mechanical properties, and furthermore, deterioration of wear resistance from this point. Therefore, Si is 0.4
~3.5%.

Mn: 0.5-1.5% Mn is actively added together with Si to deoxidize the molten metal, but if it is less than 0.5%, a sufficient deoxidizing effect cannot be obtained; If added in excess of this amount, mechanical properties, especially toughness, will deteriorate. Therefore, Mn is set to 0.5 to 1.5%.

P: 0.08% or less P is an impurity element that inevitably accompanies it, and as it causes embrittlement of the material, it is desirable to use a smaller amount in roll materials, but in practice, if it is suppressed to 0.08% or less, the above-mentioned Since the inconvenience can be tolerated, P is set to 0.08% or less.

S: 0.08% or less S is also an unavoidable impurity element that, like P, causes embrittlement of the material, so the smaller the amount, the better.
Since practical inconveniences can be tolerated by suppressing S to below, S is set to 0.08% or less.

Ni: More than 5.0% to 15.0% Ni has the effect of improving the base structure and crystallizing graphite, but if its content is less than 5.0%, the desired effect cannot be obtained. On the other hand, if the content exceeds 15.0%, retained austenite will increase, making it impossible to obtain the hardness required for a roll material and causing problems in wear resistance. Therefore N
i is more than 5.0% ~ 15. Let it be θ%.

Cr: 2.2-13.0% Cr combines with C to form highly hard chromium carbide and has the effect of improving wear resistance and toughness, but 2.2%
If the content is less than 13.0%, this effect will be small, and if it exceeds -13.0%, the tendency to whitening will be strong and graphite will be difficult to crystallize, making it impossible to obtain better wear resistance and anti-seizing effects. Therefore, Cr is set to 2.2 to 13.0%.

Note that Cr1l in the present invention needs to satisfy a weight ratio of Cl, that is, a Cr/C ratio of (1.0 to 3.5).

Mo: More than 2.0% to 10.0% Mo is an extremely important element as a component of the outer layer material of the hot rolling roll according to the present invention, and it enters the matrix and improves high temperature properties such as high temperature softening resistance. By improving the characteristics,
In addition to preventing precipitated carbides and crystallized graphite from peeling off easily at high temperatures, it also forms high-hardness molybdenum double carbides that dramatically improve wear resistance. Guarantees seizure resistance. However, if the Mo content is 2.0% or less, the desired effect cannot be obtained in the above action, whereas if the Mo content exceeds 10.0%, the above action is saturated. More than 10%
．． It is set at 0%, and more preferably from 3.0 to 8.0% in consideration of the degree of effect and economical efficiency.

Al = 0.02 to 2.5% Al is an important element that characterizes the present invention together with Mo, and adding a relatively small amount can dramatically improve heat resistance. It goes without saying that improving heat resistance further improves wear resistance and seizure resistance.

Note that Al has a graphitization promoting effect more than that of Si, and S
By adding an appropriate amount of Al together with i, it is possible to crystallize a large amount of graphite in the structure without increasing the Si content, which would lead to deterioration of mechanical properties. That is, if Al is contained in an amount less than 0.02%, these effects will be small, while if it is contained in an amount exceeding 2.5%, graphite will crystallize excessively and the base hardness will also decrease.

Therefore, Al was set at 0.02 to 2.5%.

Nb, V, WSZrs Ti: The total content of one or more of these is 1.0% or less The outer layer material of the hot rolling roll according to the present invention is substantially composed of Pa other than the component composition explained above. However, both chilled alloys and grain alloys contain Ji in addition to the above components.
b, V, W% Even if one or more of Zr or Ti is contained, if the total is 1.0% or less, it will not have an adverse effect on the desired performance.In fact, both chilled alloys and grain alloys Since it helps strengthen the casting structure by making it finer, it may be actively added.

On the other hand, if the total amount exceeds 1%, the effect will be saturated and other materials will become brittle and mechanical properties will deteriorate, so the total amount should be 1% or less.

Cr/C: 1.0 to 3.5 (wt%/wt%) Cr/
When the C ratio is less than 1.0, the amount of carbide produced is small and wear resistance deteriorates, while when the Cr/C ratio exceeds 3.5, problems arise in terms of seizure resistance. Therefore, Cr/C=1.0
~3.5.

It is also clear from FIG. 4, which will be described later, that the Cr/C ratio must be limited to 1.0 to 3.5.

Graphite: 1.0-4.0% (area ratio) Graphite in grain alloys has a lubricating effect and is said to be particularly effective in ensuring seizure resistance. Conventionally, it has been considered practically difficult to contain a large amount of Ni because it causes deterioration of wear resistance. However, in the grain alloy of the present invention, the base toughening by Mo and Al suppresses the loss of graphite, and it is possible to stably contain a larger amount of graphite than the conventional level, sacrificing wear resistance. Seizure resistance can be improved without any problems. The effect of improving seizure resistance is large when the area ratio of crystallized graphite is 1.0% or more, and conversely, when the area ratio exceeds 4.0%, wear starting from graphite becomes significant, and although it is not sufficient in terms of wear resistance. It disappears. Therefore, it is preferable that the graphite content which satisfies both abrasion resistance and seizure resistance with a suitable balance is 1.0 to 4.0% in terms of area ratio.

In addition, if the amount of graphite is 1. It is clear from FIG. 5, which will be described later, that the content is preferably 0 to 4.0%.

On the other hand, even in the case of chilled alloys, because graphite does not crystallize, there are more carbides than in grain alloys, and these carbides are difficult to peel off even at high temperatures, so wear resistance at high temperatures does not improve dramatically. It goes without saying.

The alloy having the above composition and structure defined in the present invention may be used for the entire roll or as the outer layer material of a so-called composite roll in which the outer layer material and the inner layer material are made of different materials. In this case, as in the conventional case, a strong material such as ductile cast iron, ordinary cast iron, graphite steel, etc. is selected as appropriate for the shaft core depending on the intended use.

To manufacture the hot rolling roll according to the present invention, a molten metal adjusted to have the above-mentioned composition is poured into a mold and solidified according to a conventional method. That is, for rolls made entirely of the same material, a normal casting method is used, and for composite rolls, a hollow casting method, a sliding gate method, a centrifugal casting method, etc. are used.

In the case of grain alloys, carbon is added to the molten metal to control the amount of graphite.
This does not prevent the addition of inoculants such as a-Si alloys and Fe-Si alloys.When adding inoculants to molten metal, the component composition changes with the addition of inoculants so that the final components are within the target range. It is necessary to use molten metal whose content has been corrected in advance.

The cast rolls are annealed to remove residual stress during casting and to stabilize the microstructure, and then cut and polished to the desired dimensions.

The hot rolling roll according to the present invention is suitable for use as work rolls before and after finishing hot strip mills, as well as work rolls for hot skin passes, rolls for rolling long steel, and rolls for pipe making, and is also suitable for finishing work rolls for cold strip mills. It can also be applied as a cold rolling roll such as a work roll or a wire finishing roll.

Next, the present invention will be concretely explained using Examples and in comparison with Comparative Examples.

(Example) Product trunk diameter: 750 mm, trunk length: 1800 mm, total length: 380 mm
To manufacture a centrifugally cast composite roll with a diameter of 0 m, melts of outer layer materials of various compositions are placed in a mold rotating on a centrifugal casting machine.
Cast to a wall thickness of 90°C at a temperature of around 420°C, Fe-3i alloy was used as an inoculant if necessary. After the outer layer material molten metal was completely solidified, the mold was stood vertically with the outer layer material inside, the core material molten metal was poured from above, and the upper end was covered with a riser and a heat insulating material.

After the core material molten metal has completely cooled, the roll is removed from the mold, and the outer layer material composition and graphite amount are shown in Table 1.22
A composite roll of the type shown in FIG. 1 consisting of an outer layer material 1 and a shaft core material 2 was obtained.

In addition, in Table 1, examples Nal, 6.8 and 22.23.
The case of 25.27 in which the amount of graphite is zero corresponds to a chilled alloy, and the others correspond to a grain alloy.

The obtained composite roll was subjected to strain relief heat treatment (350℃
10Hr) and texture adjustment heat treatment (420°C x 20H
r) was applied.

A wear test piece and a seizure test piece (both 100 mmφ x 30) were taken from the outer layer material of the body end of the composite roll manufactured in this way, and the wear test piece was subjected to an abrasion test as schematically shown in Fig. 2. (Stress 25 kgf/am", rotation speed 1
0 Or, p, m, test time 100 m1n, workpiece heating piece temperature 800° C.), and the wear volume after the test was measured. FIG. 2(a) is a side view of the test device, and FIG. 2(b) is a plan view. A workpiece heating piece 4 heated by a high-frequency coil 3 is rotated at a constant speed, and a roll material test piece 5 is pressed against it with a constant pressing force (P). On the other hand, for the seizure test piece, a friction test (stress of 10 kg
f/m+s”, rotation speed 1or.

The friction coefficient, which indicates the degree of adhesion between the two metals, was investigated using 10 w1n test time and 800° C. temperature of the heated piece of the workpiece. FIG. 3(a) is a side view, and FIG. 3(b) is a plan view. Components that are the same as those in FIG. 2 are designated by the same reference numerals.

In addition, SUS 304 was used as the mating workpiece heating piece 4 in all tests. The results are shown graphically in FIGS. 4 and 5.

FIG. 4 shows the wear volume and friction coefficient arranged according to the Cr/C ratio.

As a result, Cr
It has been found that when the Cr/C ratio is less than 1.0, the seizure resistance is good but the wear resistance is poor, and when the Cr/C ratio exceeds 3.5, the wear resistance is good but the seizure resistance is poor. Ru.

In other words, the range in which the wear resistance and seizure resistance of both grain alloys and chilled alloys can be satisfactorily balanced is Cr.
/C=1.0-3.5.

FIG. 5 shows the influence of crystallized graphite and the amount of Mo added on the wear resistance and seizure resistance when Cr/C=1.0 to 3.5.

The effect of the amount of Mo added is approximately 2 the amount of graphite in Table 1.
．． Align to 6% and different Mol examples 11h7.14.17
．． The numbers in Figure 18 indicate examples of the present invention.

According to this result, Cr/C=1.0 to 3.5 is satisfied, and the amount of crystallized graphite in the grain alloy is 1.0 to 4 in terms of area ratio.
．． It was demonstrated that those with 0 showed even better wear resistance and seizure resistance.

Regarding the amount of Mo added, if MO is less than 2.0%, the effect of improving wear resistance and seizure resistance is small;
It can be seen that if it exceeds this, these improvement effects are saturated, and it is by no means preferable when considering graphite crystallization, economic efficiency, etc.

Table 2 shows the comparison roll l1hl, 7 and the roll of the invention round 8.
．． 12.17.21.23.24.25.27 shows the hardness (Hv) at room temperature and high temperature.

In addition, N11l, 8.23.25.27 is a chilled alloy,
Others are grain alloys.

The hardness of the roll of the present invention is higher than that of the comparative roll at both room temperature and high temperature, and there is little decrease in hardness.Table 2 (Effects of the Invention) As explained above, according to the present invention, chilled alloy Regardless of the form of grain-based alloy, it is possible to create a rolling roll that has both excellent wear resistance and seizure resistance, and it has excellent durability even in recent harsh hot rolling conditions. In addition to this, it also brings about industrially useful effects, such as guaranteeing good product quality and superior safety.

[Brief explanation of the drawing]

1st WJ is a schematic diagram showing an example of the structure of a composite roll for rolling.
Figure 4 is a graph showing the relationship between the Cr1C ratio and wear resistance and seizure resistance in the outer layer material of the composition of the roll of the present invention; and Figure 5 is a graph showing the relationship between the wear resistance and seizure resistance of the roll of the present invention. 2 is a graph showing the relationship between the crystallized graphite content ratio (area ratio of cross section & 11 weaves) and wear resistance and seizure resistance in the outer layer material having the component composition according to the above. 1: Outer layer material 2: Shaft core material

Claims (6)

[Claims] (1) At least the outer layer has a weight ratio of C: 2.2 to 3.7%, Si: 0.4 to 3.5%, and Mn.
: 0.5-1.5%, P: 0.08% or less, S: 0.0
8% or less, Ni: more than 5.0% to 15.0%, Cr: 2.
2-13.0%, Mo: more than 2.0%-10.0%, Al
: 0.02 to 2.5%, balance: Fe and unavoidable impurities, and is composed of an alloy satisfying Cr/C=(1.0 to 3.5). Roll for rolling. (2) The hot rolling roll according to claim 1, wherein the outer layer is a chilled alloy. (3) The hot rolling roll according to claim 1, wherein the outer layer is made of a grain alloy. (4) At least the outer layer has a weight ratio of C: 2.2 to 3.7%, Si: 0.4 to 3.5%, and Mn.
: 0.5-1.5%, P: 0.08% or less, S: 0.0
8% or less, Ni: more than 5.0% to 15.0%, Cr: 2.
2-13.0%, Mo: more than 2.0%-10.0%, Al
: 0.02 to 2.5%, and the total of one or more of Nb, V, W, Zr, and Ti is 1.0% or less, and the balance consists of Fe and inevitable impurities, and Cr/C= A hot rolling roll comprising an alloy satisfying (1.0 to 3.5). (5) The hot rolling roll according to claim 4, wherein the outer layer is a chilled alloy. (6) The hot rolling roll according to claim 4, wherein the outer layer is made of a grain alloy.