JPH08260100A - Work roll for cold rolling excellent in seizing resistance - Google Patents

Abstract

PURPOSE: To improve the seizing resistance of a work roll while its grindability is secured by controlling the compsn. of a rolling roll of a high carbon chromium steel used at the time of subjecting a common steel thin sheet or a stainless steel thin sheet to cold rolling by a tandem rolling mill, particularly, the compositional ratio of the content of Cr to the content of C and the area ratio of M3 C type carbides occupied in the base of the roll. CONSTITUTION: The content of C in a high carbon chromium steel forming a roll is regulated to 1.0 to 3.5wt.%, furthermore, it has a compsn. in which the content of Cr is regulated to 1 to 4 by C ratio (Cr/C), and the area ratio of M3 C type carbides in the structure of the roll is regulated to 3 to 20%. Since a seizing phenomenon in the process of rolling starts from the structure of the roll base high in affinity with a rolling stock and carbides have an operation of stopping the growth of seizing, the grain size thereof is preferably regulated to about 1 to 5μm. Moreover, the other elements such as Si, Mn, Mo, V or the like may suitably be added thereto for the purpose of securing its hardenability and toughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a work roll for cold rolling having excellent seizure resistance, particularly for cold rolling of steel sheets such as ordinary steel and stainless steel, which has excellent seizure resistance and is ground at the same time. The work rolls that ensure the sex.

[0002]

2. Description of the Related Art Conventionally, as a performance required for a work roll for cold rolling, it has been emphasized that it has excellent wear resistance. On the other hand, from the point of view of actual use, it is important that the roll surface be rapidly imparted with a predetermined profile prior to use, that is, exhibit excellent grindability. However, this grindability and wear resistance are contradictory properties and are considered to be incompatible. for that reason,
Since the roll is also a kind of processing tool, conventionally, in general, abrasion resistance is generally secured even if the grindability is sacrificed.

In terms of material, 5% Cr steel having a composition of C: 0.8% and Cr: 5% has been frequently used as a specific material. In recent years, from the perspective of further improving wear resistance, semi-high-speed steel (eg C: 1%, Cr: 6%, Mo: 3%, V: 1
%), High chrome steel (eg C: 1%, Cr: 10%, Mo: 1%)
Is being used.

However, the following problems are observed in such a conventional technique. When performing high-speed cold rolling at a rolling speed of 1500 to 2000 m / min or higher with a tandem mill, and for stainless steel (especially SUS430 material), perform high-speed cold rolling at a rolling speed exceeding 300 m / min. In this case, rolling material surface defects called seizure (or friction pickup, heat streak, etc.) may occur. Such seizure is more likely to occur under high-pressure / high-speed rolling conditions, which is a bottleneck in improving productivity.

Up to now, the following measures have been taken against such a problem. 1) As a matter of course, first, it is conceivable to relax the operating conditions (for example, the rolling reduction and the speed), but this sacrifices the productivity and hinders the original purpose of high-speed rolling.

2) For example, it has been attempted to improve the lubricity of rolling oil by using a synthetic ester as a base oil and further by using various additives, but such measures require capital investment. In some cases, it is not a simple means. In addition, the effect is not sufficient at present, and it is still under research and development.

Even under such a current situation, however, it can be said that there is almost no response from the roll side. There are very few studies on lubrication performance such as seizure resistance of rolls.

By the way, in tools for forging and pressing such as dies, a surface modification layer made of a carbide or nitride of a hardening element typified by titanium or vanadium is provided by a CVD, PVD or TRD process. Tool materials have been developed that have not only excellent wear resistance such as tool materials, cemented carbide and ceramic materials, but also good lubricity.

However, when it is considered to apply such a material to a tandem rolling roll, it is extremely difficult to put it into practical use due to problems such as difficulty in manufacturing and high cost. Further, from the viewpoint of roll grindability, none of the above methods is practical.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to prevent the seizure which occurs in a rolled material and a roll when cold rolling a plain steel sheet or stainless steel in a tandem rolling mill. It is to develop a technology that can prevent the improvement and improve the productivity by facilitating the grinding.

[0011]

Means for Solving the Problems The inventors of the present invention have made various studies in order to solve such problems, and have completed the present invention by obtaining the following knowledge.

For example, in the case of a sialon-based roll which is a conventional cold rolling roll, it has an abrasion resistance due to its high hardness as an original effect, and a seizure resistance due to a nonmetallic component as a next effect. It has excellent sex. However, the grindability is extremely poor.

In addition, although there are roll materials containing 3 to 20% of carbides, such as semi-high-speed steel, there is a conventional roll material.
[Iron and steel, vol.81 (1995) No.1, p.64-69], its carbide has a high hardness with addition of alloying elements such as V, Mo and W from the viewpoint of improving wear resistance. It was found that MC, M ₆ C, M ₇ C _3, etc. were the main constituents, and the roll material containing such hard carbide had extremely poor grindability.

That is, the conventional roll material requires a long time for grinding, and it is easy to generate a grinding scratch, and seizure occurs from this scratch, which rather deteriorates the seizure resistance.

In the case of M ₃ C type carbide, the area% is 3 to 20.
It has been proved that even if the content of Ni is 0.1%, it is effective in exerting the seizure stopping effect. The type of carbide is mainly M ₃ C, and C: 1.0〜
It has been found that 3.5% and a Cr content of 1 to 4 in a C ratio (Cr / C) are effective for a roll composition having grindability.

In order to simultaneously exhibit the grindability and the seizure stopping action, which are contradictory characteristics as described above, it is unexpectedly effective to use a composition satisfying the above and, and It has been found that the synergistic effect improves both properties to the extent not previously seen. Other elements may be added appropriately in consideration of hardness and material strength.

Here, the gist of the present invention is that, in wt%, C: 1.0 to 3.5%, and the Cr content is the C ratio (Cr / C).
Has a steel composition of 1 to 4 and contains M ₃ C type carbide in area%
It is a work roll for cold rolling which is excellent in seizure resistance and at the same time secures grindability, which is characterized by containing 3 to 20% by weight.

[0018]

Next, the reason why the present invention is limited as described above will be explained together with its operation.

(1) Reasons for limiting types of carbides In the present invention, attention is paid to the M ₃ C type as a carbide. As described above, although carbides such as MC, M ₆ C, and M ₇ C ₃ are certainly hard, the use of such carbides, in turn, results in extremely poor roll grindability. Moreover, if the surface of such a high-hardness carbide is ground, seizure due to grinding scratches will occur instead.

Particularly in the case of the present invention, since it is intended for high carbon type rolls, M ₃ C type carbides are likely to be formed, and under ordinary manufacturing conditions and steel composition, MC, M ₆ C, M ₇ C ₃ etc. Carbides are formed in a very small amount, for example, 1% or less in area%. The particle size of such a carbide is not particularly limited, but in the preferred embodiment of the present invention, it is preferably limited as follows.

(2) Reason for limiting carbide grain size The general role of the carbide contained in the rolling roll is to improve wear resistance (because the hardness is higher than that of the matrix structure).
However, in the present invention, attention is paid to the carbide of the roll from the viewpoint completely different from this property, that is, from the viewpoint of seizure resistance. During cold rolling, the rolled material and the roll are locally in direct contact with each other, and transfer of the rolled material to the roll surface, so-called seizure often occurs. Explaining the mechanism of seizure from the microstructure of the roll, seizure starts from the matrix structure having a strong affinity for the rolled material, and the carbide has a function of stopping its growth.

In order to exert this effect, it is preferable that the grain size of the carbide is 1 μm or more. The upper limit is not particularly limited,
The thickness is preferably 20 μm or less, which is restricted due to grindability, accident resistance, and roll manufacturing difficulty. More preferably, it is 1 to 5 μm. In this respect, the conventional work roll for cold rolling 5%
In Cr steel, the average grain size of carbides is 1 μm or less.

(3) Reason for limiting carbide area% In order to realize seizure resistance, the above grain size is satisfied and a considerable amount of carbide is required. This is because as the amount of carbide increases, the spacing between each carbide becomes narrower,
The seizure growth is stopped faster and more reliably.

If the carbide area% is less than 3%, such an effect is small, and it is insufficient to obtain the effect of preventing seizure in rolling in an actual production line. The effect is up to 20%, and even if the carbide area is increased from this, there is no big difference in the total number of carbides, only the size of the carbide itself increases, and the (average) spacing between the carbides is increased. Is unchanged. Larger size and excessive increase of carbide impairs grindability,
There is a detrimental effect that promotes the removal of carbides during rolling, while also promoting segregation in roll production, induction of quench cracks during heat treatment,
The upper limit is 20% by area because it makes manufacturing difficult.
It is preferably 5 to 15 area%.

(4) Reasons for limiting components C: 1.0 to 3.5% C is an element necessary for forming carbides and ensuring matrix hardness. In the present invention, the amount of carbide is limited in order to secure the amount of carbide (while maintaining the relationship with the amount of Cr described later). 1.
If it is less than 0%, the amount of M ₃ C-type carbides of 3 μm or more, which is preferably 1 μm or more, cannot be secured, and seizure resistance becomes insufficient. In addition, as described above, addition of more than 3.5% by weight is not expected to improve seizure resistance, but rather leads to coarsening of eutectic carbides, etc., which deteriorates grindability and causes frequent scratching, causing seizure resistance. Will be deteriorated. Not only that, but it can also make manufacturing difficult. Preferably 1.0 to 2.5%, more preferably 1.0 to 2.0%
Is.

Cr: Cr / C = 1 to 4 Cr is a carbide-forming element, and is added in the present invention in order to secure the above-mentioned amount of carbide, but in order to specify the kind of carbide to be formed, the ratio with C is specified. (Cr / C) is limited. Cr / C
When the ratio is 4 or less, the main carbides are M ₃ C carbides with hardness Hv: about 1000, whereas when the ratio exceeds 4, the hardness is higher (Hv: about 1800) M ₇ C. ₃ Carbide is the main constituent, which deteriorates the grindability and induces the generation of grinding scratches. If the ratio is less than 1, hardenability is poor,
Base hardness becomes insufficient. Preferably, this ratio is between 1 and
It is 3.

Other elements are appropriately added for the purpose of ensuring hardenability and toughness. In the present invention, the steel composition is not limited to a specific one, but in practice, the following steel compositions are preferable in terms of weight%. The preferred range is shown in parentheses.

C: 1.0 to 3.5% (1.0 to 2.0%), Si: 0.1
~ 1.5% (0.1 to 1.0%), Mn: 0.1 to 1.5% (0.1 to 1.0%)
%), P: 0.03% or less, S: 0.03% or less, Cr: 1.0
~ 14% (1.0 to 6.0%), Mo: 0 to 1.5% (0.2 to 1.0%)
%), V: 0 to 1.0% (0.2 to 0.5) balance Fe and inevitable impurities.

The reason why the steel composition is limited as described above in the preferred embodiment of the present invention is as follows. Si: Add 0.1% or more as a deoxidizer. On the other hand, if it exceeds 1.5%, embrittlement is promoted. Preferably, the upper limit is 1.0%
And

Mn: Compounded as a deoxidizer, and is required to be 0.1% or more especially for improving hardenability. However, if it exceeds 1.5%, embrittlement is promoted, so the upper limit is made 1.5%, preferably 1.0%.

P and S: Both of them are limited to 0.03% or less as impurities. Cr: Cr has the same purpose of addition as previously described, but Cr
The ratio of / C is 1.0 to 14% in order to secure 1 to 4, and preferably 1.0 to 6.0%.

Mo: An optional additional element added as necessary, and is added in an amount of 0.2% or more in order to prevent pearlite transformation during quenching, improve hardenability, and exert an effect of increasing temper softening resistance. Is good. However, if it exceeds 1.5%, hard carbides such as MoC will increase and the grindability will be impaired, so the upper limit is made 1.5%. Preferably 0.2-1.
It is 0%.

V: 0.2% or more may be added to strengthen the matrix structure. However, if it exceeds 1.0%, the extremely hard carbide VC increases and the grindability is impaired. Preferably
0.2 to 0.5%. Next, the working effects of the present invention will be described more specifically by way of examples.

[0034]

【Example】

(Example 1) A rolling experiment was conducted using nine types of rolls shown in Table 1 to investigate the influence of the amount of roll carbide on the seizure resistance.

No. 1 and No. 9 are 5% Cr steel and semi-high speed steel which are frequently used in the cold rolling used in the actual production line and used for comparison. Nos. 2 to 8 are rolls in which the amount of carbide is adjusted from 2 area% to 25 area% by designing the amounts of C and Cr.

The conventional example is a semi-high speed steel roll,
It contains MC type carbide as carbide. The area-equivalent diameter of carbides other than No. 1 was 1 to 20 μm.

A 0.4 mm thick and 15 mm wide aluminum-killed steel annealed tempering material was used as the rolled material, and a rolling oil was circulated and used by keeping an emulsion of 5% beef tallow at 50 ° C. The speed of the upper roll, which is an evaluation roll, was set to 143 m / min, and the feed rate of the rolled material was set to 1/10 of the roll speed in order to easily seize.

FIG. 1 shows the seizure resistance of each roll arranged by the rolling reduction. The numbers in the figure show the steel numbers in Table 1. Steel No. 1 which is the base steel and Steel No. 2 having a carbide content of 2 area% have a seizure limit of 8%, whereas Steel Nos. 3 to 8 containing a carbide content of 3 area% or more The result was that the rolling reduction was 10 to 16%, which was excellent in seizure resistance.

Steel N with a carbide content of 20 area% and 25 area%
No significant difference was observed in o.7 and 8, and it became clear that the effect was saturated when the amount of carbide was 20 area%. On the other hand, when an evaluation test of the grindability of these steels was performed under the following conditions,
The results shown in FIG. 2 were obtained. However, the grindability of this example was relatively evaluated by the current value during cutting.

From the results shown in FIG. 2, it can be seen that the roll material according to the present invention has a grindability equal to or better than that of the conventional roll material. Grindstone type: GC Depth of cut: 20 μm Test material: φ76 × L Grindstone width: 30 mm

[0041]

[Table 1]

[0042]

As described above, according to the present invention, seizure, which is a problem in cold rolling, can be achieved by increasing the amount of carbides in the roll steel composition within the range that does not impair the grindability. It has become possible to prevent The improvement of the rolling oil that has been taken so far may require the entire equipment to be remodeled, which incurs a high cost, but if the roll itself can be improved, there will be no such concerns, so seizure prevention Although it is an inexpensive means as a countermeasure, the present invention immediately leads to speedup and improvement in productivity.

[Brief description of drawings]

FIG. 1 is a graph showing seizure resistance performance of each roll arranged by rolling reduction.

FIG. 2 is a graph showing evaluation of grindability by a grinding test in Examples.

Claims (1)

[Claims] 1. A steel composition having a weight ratio of C: 1.0 to 3.5%, a Cr content of 1 to 4 in a C ratio (Cr / C), and M ₃ C.
A work roll for high-carbon cold rolling which is excellent in seizure resistance and at the same time secures grindability, characterized in that it contains 3 to 20% by area type carbide.