GB2367075A

GB2367075A - Roll for rolling

Info

Publication number: GB2367075A
Application number: GB0122689A
Authority: GB
Inventors: Yasuhiro Jinbo
Original assignee: Kanto Special Steel Works Ltd
Current assignee: Kanto Special Steel Works Ltd
Priority date: 1999-02-26
Filing date: 2000-02-23
Publication date: 2002-03-27
Also published as: DE10084289T1; KR20010103013A; TW446588B; AU2690000A; BR0008967A; WO2000051756A1; GB0122689D0

Abstract

A roll for rolling which has a base material made from a steel containing 0.60 to 1.1 % of C, 0.15 to 3.0 % of Si, 0.15 to 3.0 % of Mn, 3.0 to 12.0 % of Cr, 0.5 to 5.0 % of Mo and 0.5 to 10 % of Co and, on the surface thereof, a hard coating film formed through a surface modification treatment using the PVD method or the CVD method, wherein carbide grains being dispersed on the surface of the basic material to be treated have a maximum equivalent grain diameter of 20 žm or less. The roll has excellent resistance to wear, seizure and accident, and also is excellent in grindability, and moreover can be manufactured at a low cost, which result in marked improvement in the productivity and the surface quality of steel plates.

Description

2367075

Specification

Roll For Rolling Technical Field

This invention relates to a roll for rolling. More specifically, this invention relates to a roll for rolling which is suitable for use in the cold rolling of steel sheet of, for example, cominon steel or stainless steel or the like and which improves the productivity of steel sheet and which improves the surface quality lo of the resulting steel sheet.

Background Art

A roll for cold rolling which is used as a tool at the time of manufacture of steel sheets naturally needs to have excellent wear resistance. A roll for cold 15 rolling is also required to have excellent grindability such that a prescribed surface condition and roughness can be imparted thereto, and it is required that the damage thereto be small when accidents such as the breakage of a plate occur during rolling, i.e., it is required to have excellent resistance to accidents.

In recent years, with the objective of obtaining great improvements in 20 productivity, operation has been increasing under severe conditions of high speed and heavy reduction in which the rolling speed and reduction are increased. When operation is carried out under such severe conditions, the temperature increases at the interface between the roll for cold rolling and the material being subjected to rolling, and it becomes easy for the oil film at the interface to break 2-5 and for seizing to occur. Therefore, in a roll for cold rolling, it is required that the roll for cold rolling itself not easily undergo seizing, i.e., it must have resistance to seizing.

In addition, in order to manufacture a rolled material having particularly good surface quality, it is important to transfer the surface condition of the roll for cold rolling to the material being rolled as accurately as possible by making the thickness of the oil film at the interface of the roll for cold rolling and the material being rolled as thin as possible.

S Thus, a roll for cold rolling is required to have excellent wear resistance in which the surface condition and roughness can be maintained over a long period of time, and excellent seizing resistance such that seizing does not take place even when the thickness of the oil film is thin.

From in the past, forged steel rolls made from high-Cr and high-speed lo steels (referred to below in this specification for short as "highspeed") have come to be much used as a roll for cold rolling. By gradually increasing the degree of alloying, the wear resistance and resistance to accidents of these forged rolls have been increased, and besides, a required grindability must be sufficiently guaranteed.

15 In order to guarantee a wear resistance and resistance to seizing such that great increases in productivity and great improvements in the surface quality of steel plate can be realized, it has been proposed to employ ceramic rolls or cemented carbide rolls of solid body or having a composite structure of a steel core as a small diameter or short roll for cold rolling.

20 However, it is not possible to realize great increases in productivity or marked improvements in the surface quality of steel given the extent of wear resistance and resistance to accidents which can be obtained by high-Cr and high speed forged steel rolls.

Furthennore, although ceramic rolls and cemented carbide rolls have a 2 5 desired wear resistance and resistance to seizing, they essentially have poor ductility, and their resistance to accidents is poor. Furthermore, ceramic rolls and cemented carbide rolls are difficult to grind, plus they are expensive.

Accordingly, in actuality, it is difficult to use these rolls in cold rolling.

Disclosure of the Invention

The object of the present invention is to provide a roll for rolling of steel sheet and particularly a roll for cold rolling of thin steel sheet, which has excellent wear resistance and seizing resistance and which is also excellent with 5 respect to resistance to accidents and grindability and is also inexpensive with great improvements in productivity and great improvements in the surface quality of thin steel plates.

In order to solve the above-described problems, the present inventors perceived of farming a hard coating by performing surface modification lo treatment of the surface of a roll made from a steel substrate. This surface modification treatment is already widely carried out in fields other than rolls for rolling, such as in the fields of various cutting tools, metal molds, and the like. However, even if a hard coating is formed on the surface of a roll for rolling by surface modification treatment, under conditions in which a high load and a high

15 slipping friction occur such as during cold rolling, the hard coating which is formed ends up easily peeling off. For this reason, up to the present, there has been almost no use of rolls on which surface modification treatment has been performed as rolls for cold rolling. The one exception is a roll plated with hard Cr which has been used a roll for cold rolling. Elongation of the life span of a 2o roll can be achieved by its excellent wear resistance. However, even with this roll plated with hard Cr, during rolling, the Cr plating ends up peeling off in portions, and an excellent wear resistance and seizing resistance of a level which can provide great increases in productivity and great increases in the surface quality of steel plate are not obtained at all.

25 Therefore, for reasons to be described below, the present inventors focused on the PVD method and the CVD method as surface modification methods other than the plating method, which fundamentally has an inadequate adhesive strength. In actuality, cutting tools and metal molds and the like have already been realized in which a substrate of a prescribed steel composition is coated with a hard coating by these methods. However, according to the investigations of the present inventors, even if a hard coating is formed by surface modification treatment by the PVD method or the CVD method, the adhesive strength between 5 the matrix and the hard coating is inadequate under severe conditions corresponding to cold rolling, and it was found that considerable improvements are necessary for their practical application.

The present inventors perfori-ned intense research in a basic reason why a hard coating formed by surface modification treatment by the PVD or the CVD 1 o method ends up peeling off. As a result, they obtained the belowdescribed new knowledge (i)-(vi) and completed the present invention.

(i) This peeling is strongly influenced by the maximum equivalent particle diameter dmax of carbides which are dispersed on the surface of the substrate. The maximum equivalent diameter d.a, of the carbides means the maximum value of 15 the equivalent particle diameter VSc obtained based on the area Sc of the carbide particles. The area of the carbide particles is found by image analysis using the surface of the roll substrate as a surface for investigation. The maximum equivalent particle diameter d.a., of carbides of a steel substrate to be subjected to surface modification by the conventional PVD method or CVD method was on 20 the order of 30-50 micrometers.

Specifically, if the maximum equivalent particle diameter dmax of carbides is less than or equal to 20 micrometers, the adhesion between the substrate and the hard coating is increased, and the hard coating does not peel off even under rolling conditions in which a high load and high slipping friction occur.

25 Therefore, even in cold rolling of steel sheet such as common steel or stainless steel or the like, great increases in productivity and great increases in the surface quality of steel plates can be achieved.

(ii) This peeling is caused by embrittlement due to a change in the structure of the surface layer of the substrate during high load and high slipping friction conditions.

By optimizing the composition of the substrate so that it is difficult for the surface layer of the substrate to undergo a change in structure and particularly to 5 optimize any of the C content, the Si content, and the Ni content, the adhesion between the substrate and the hard coating can be made adequate and also can be maintained for a long period even under severe conditions. Therefore, even in the cold rolling of steel sheet such as plain steel or stainless steel or the like, great increases in productivity and great increases in the surface quality of steel plate lo can be achieved.

(iii) This peeling is caused by the difference between the stiffness of the carbides in the substrate at the interface between the hard coating and the substrate and the stiffness of the matrix.

By optimizing the ratio (Cr/C) of the C content of the substrate and the Cr 15 content which is determined to be balanced therewith, carbides are softened, and an adequate adhesive strength between the substrate and the hard coating can be guaranteed even during cold rolling under severe conditions. Therefore, in cold rolling of steel sheets such as common steel or stainless steel or the like, great increases in productivity and great improvements in the surface quality of steel 20 plate can be achieved.

(iv) This peeling is caused by embrittlement due to a change in the structure of the surface layer of the substrate under high load and high slipping friction conditions.

By optimizing the composition of the substrate, and specifically by adding 25 an appropriate amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta so as to make it difficult for a change in the structure of the surface layer of the substrate to take place, adhesion between the substrate and the hard coating can be made adequate and also can be maintained for long periods even under severe conditions. Therefore, in cold rolling of steel sheet such as common steel or stainless steel or the like, great increases in productivity and great improvements in the surface quality of steel plate can be achieved.

5 (v) This peeling is caused by tensile stresses remaining in the substrate surface prior to surface modification when using a roll for cold rolling having a relatively small diameter of 300 millimeters or less.

By adjusting and improving the chemical composition of the substrate and by making the stresses in the substrate surface after hardening and tempering be io compressive stresses, the adhesive strength between the substrate and the coating can be made strong, and peeling of the hard coating can be prevented even under severe conditions of a high load and high slipping friction. Therefore, great increases in productivity and great improvements in the surface quality of steel plate can be achieved even during cold rolling of steel sheet such as common is steel or stainless steel or the like.

(vi) This peeling is caused due to the difference in stiffness between the carbides in the substrate at the interface between the hard coating and the substrate, and the stiffness of the matrix structure in the substrate.

Therefore, by improving the chemical composition of the substrate, and 20 specifically by using a high-speed steel in which hard carbides are finely dispersed as a base and by adding an appropriate amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta, the adhesive strength between the substrate and the hard coating can be adequately maintained, and peeling of the hard coating can be prevented even under high 25 load and high slipping friction rolling conditions. Therefore, great increases in productivity and great improvements in the surface quality of steel plate can be achieved even in cold rolling of steel sheet such as common steel or stainless steel or the like.

The essence of the present invention is a roll for rolling comprising a steel substrate and a hard coating formed on the surface of the substrate by surface modification treatment, characterized in that the maximum equivalent particle diameter dmaxof carbides dispersed on the surface of the substrate is at most 20 5 micrometers.

In. a roll for rolling according to the present invention, an example of a substrate contains C: 0.60 - 1.1 % (below, in this specification, unless otherwise specified, 'W' means "mass percent"), Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 3.0 - 12.0%, Mo: 0.5 - 5.0%, and Co: 0.5 - 10%.

10 From a different standpoint, the present invention is a roll for cold rolling characterized by comprising a steel substrate containing C: at least 0. 30% and less than 0.60%, Si: at least 0. 15% and less than 0.30%, M-n: 0. 15 - 3. 0%, Ni: 0.3 - 3.0%, Cr: 2.0 - 8.0%, and Mo: 0.2 3.0%, and a hard coating formed on the surface of the substrate by surface modification treatment.

15 From another standpoint, the present invention is a roll for rolling characterized by comprising a steel substrate including C: 0.60 - 3.5%, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Mo: 0.5 - 5.0%, Co: 0.5 - 10%, with a ratio of Cr to C (Cr/C) of I - 4, and a hard coating formed on the surface of the substrate by surface modification treatment.

20 From another standpoint, the present invention is a roll for rolling characterized by comprising a steel substrate containing C: 0.3 - 1.0%, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 2.0 -8.0%, Mo: 0.2 - 3.0%, V: 0.05 - 2.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta. in a total amount 0.01 - 0.50%, and a hard coating formed on the surface of the 25 substrate by surface modification treatment.

From another standpoint, the present invention is a roll for rolling characterized by comprising a steel substrate containing C: 0.4 - 1.0%, Si: 0. 15 - 1.0%, Mn: 0. 15 - 1.0%, Cr: 1.0 - 3.0%, Mo: 0. 15 - 3.0%, V: 0.5 - 5.0%, and Co:

0.50 - 10.0%, with zero stress or a compressive stress being imparted to the surface of the substrate, and a hard coating formed on the surface of the substrate by surface modification treatment.

From another standpoint, the present invention is a roll for rolling 5characterized by comprising a steel substrate containing C: 0. 8 - 1.8%, S i: 0. 15 - 3.0%, Mn: 0. 15 -3.0%, Cr: 2.0 - 8.0%, Mo: 2.0 - 10.0%, V: 1.0 - 5.0%, Co: at most 10.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta in a total amount of at most 1.0%, and a hard coating formed on the surface of the substrate by surface modification treatment.

10 In a roll for rolling according to these inventions, the PVD method or the CVD method will be given as examples of the surface modification treatment.

Brief Explanation of the Drawings Figure 1 is a graph showing the results of a test evaluating adhesion in Example 1.

15 Figure 2 is a graph showing the results of a test evaluating adhesion in Example 2.

Figure 3 is a graph showing the results of a test evaluating adhesion in Example 3.

Figure 4 is a graph showing the results of a test evaluating adhesion in 2 o Example 4.

Figure 5 is a graph showing the results of a test evaluating adhesion in Example 5.

Figure 6 is a graph showing the results of a test evaluating adhesion in Example 6.

Detailed Explanation of the Invention Below, forms of carrying out a roll for rolling according to the present invention will be explained in detail with respect to each invention.

(First Embodiment) [Substrate] A roll for rolling according to this invention has a steel substrate.

Specifically, a roll for rolling according to this invention contains C: 0.60 - 1. 1 5 Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 3.0 - 12.0%, Mo: 0.5 - 5.0%, and Co: 0.5 - 10%. Below, the reasons for the limitations on the composition of the substrate will be explained.

C: 0.60 - 1.1% C: has a large effect both on the hardness of the matrix of the substrate and lo on the formation of carbides. The hardness of the matrix is controlled primarily by the amount of C in solid solution. If the C content is less than 0.60%, the hardness of the matrix is inadequate, while if the C content exceeds 1. 1 %, due to the relationship with the content of the below-described alloying elements (primarily Cr), coarse carbides having a maximum equivalent particle diameter 1-5 dmax of greater than 20 micrometers solidify, and the adhesion of the hard coating formed on the substrate by surface modification treatment deteriorates. Therefore, in this invention, the C content is defined as at least 0.60% and at most 1. 1 %. From the same viewpoint, the lower limit on the C content is preferably 0.7%, and the upper limit is preferably 1.0%.

20 Si: 0.15 - 3.0% Si is included as a deoxidizing agent. In addition, as described further on, a substrate according to this invention normally undergoes high temperature tempering treatment at greater than 400'C prior to surface modification treatment, so it is included in order to increase resistance to softening during high 25 temperature tempering. From these standpoints, in this invention, at least 0. 15% of Si is included. However, if the Si content exceeds 3.0%, hot workability and toughness decrease. Therefore, in this invention, the Si content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the lower limit on the Si content is preferably 1.0%.

Mn: 0.15 - 3.0% In this invention, Mn is included for the same objectives as Si. For this purpose, in this invention, the Mn content is defined as at least 0. 15 % and at most 5 3.0%. From the same standpoint, the lower limit on the Mn content is preferably 0.5%, and the upper limit is preferably 2.0%. Cr: 3. 0 - 12.0% Cr is a carbide-forming element. By including at least 3.0%, there is the effect that fine carbides precipitate during tempering and softening is suppressed.

lo However, if the Cr content exceeds 12.0%, coarse carbides having a maximum equivalent particle diameter d.,_, of greater than 20 micrometers solidify. Therefore,, in this invention, the Cr content is defined as at least 3.0% and at most 12.0%. From the same standpoint, the upper limit on the Cr content is preferably 10.0%.

15 Mo: 0.5 - 5.0% By making the Mo content at least 0.5%, the resistance to softening during tempering is increased. However, if the Mo content exceeds 5.0%, toughness deteriorates. Therefore, in this invention, the Mo content is defined as at least 0.5% and at most 5.0%. From the same standpoint, the upper limit on the Mo 20 content is preferably 2.0%.

Co: 0.5 - 10% If the Co content is at least 0.5%, the aggregation of carbides during high temperature tempering is delayed, and softening is suppressed. This softening suppressing effect is adequate at 10%, and addition in excess of this level merely 25 increases costs. Therefore, in this invention, the Co content is defined as at least 0.5% and at most 10%. From the same standpoint, the upper limit on the Co content is preferably 5%.

In order to increase the hardenability of the substrate, to suppress softening during tempering, to refine carbides, and the like, a substrate according to this invention may if necessary contain Ni: at most 2%, W: at most 2%, and V: less than 0.8% as optional added elements.

In addition to the above, Fe and unavoidable impurities are present.

5 In this manner, a substrate according to this invention has a steel composition, so it has excellent grindability and a low cost.

In addition, a substrate according to this invention undergoes tempering treatment at a temperature greater than the treatment temperature of the below described surface modification treatment (such as a temperature exceeding lo 400T). It is preferable from the standpoint of wear resistance that the surface of the substrate and the vicinity thereof after tempering treatment have at least a prescribed hardness. Here, a prescribed hardness means a hardness such that the substrate itself does not undergo plastic deformation even under the action of a heavy load during rolling, or a hardness of the substrate such that indentation 15 marks are not formed in the surface modified roll by foreign matter which comes in during rolling. Specifically, it is HS 70.

[Surface modification treatment, hard coating] A roll for rolling according to this invention is one on which surface modification treatment has been carried out and in which a hard coating is formed 20 on the surface of the substrate.

In this form of carrying out the invention, the surface modification treatment is carried out by the PVD method (physical vapor deposition method) or the CVD (chemical vapor deposition method). In general, methods of surface modification other than the PVD method and the CVD method include plating, 25 thermal spraying, the TRD method (thermoreactive deposition method), and the like. Among these, plating and thermal spraying fundamentally provide a relatively low adhesive strength between the coating and the substrate, and under rolling conditions in which high degrees of load and slipping friction act such as during cold rolling, a coating formed by plating or thermal spraying ends up easily peeling off, so it can not withstand actual use. On the other hand, in the TRD method, a substrate is treated at a high temperature of greater than 800'C. For this reason, if surface modification treatment is carried out after finishing the 5 substrate into a roll, the steel composition of the substrate undergoes transformation, dimensional changes become large, and it is inappropriate for a roll for rolling which requires high dimensional accuracy.

In contrast, the treatment temperatures for the PVD method and the CVD method are both normally 200 - 400T, and a coating having an adequate 1 o adhesive strength with respect to a substrate having the above- described composition can be formed, and it does not peel off even under severe cold rolling conditions.

As the PVD method, vacuum vapor deposition, sputtering, and ion plating can be employed. As the CVD method, it is more preferable to use the plasma 15 CVD method which is characterized by treatment under a lower temperature and lower pressure (the lower limits are respectively 200'C and one Torr) compared to the widely used conventional CVD method.

[Maximum equivalent particle diameter dmax of carbides in the substrate surface] As stated earlier, cutting tools and metal molds in which surface 20 modification treatment by the PVD method or the plasma CVD method is carried out on a substrate made from an alloy tool steel or a high-speed steel such as SKD I I or SKH 5 1, which are classified as tool steels by JIS standards, are already known. However, the carbides present in the surface of the substrates of these cutting tools or metal molds are normally coarse carbides having a 25 maximum equivalent particle diameter of 30 - 50 micrometers. If they are used as is for a roll for rolling, under rolling conditions in which a high load and high slipping friction act, such as during cold rolling, due to the difference in stiffness between the coarse carbides and the matrix, the coating ends up peeling off.

Therefore, in this invention, in order to guarantee that the coating has an adequate peeling resistance, the maximum equivalent particle diameter d.. of carbides in the surface of the substrate is limited to at most 20 micrometers. From the same standpoint, the maximum equivalent particle diameter d.. of the carbides is s preferably at most 15 micrometers.

By limiting the maximum equivalent particle diameter d.. of carbides in the surface of the substrate to at most 20 micrometers, grinding scratches in the surface of the substrate can also be prevented. Namely, prior to surface modification treatment, the substrate is subjected to grinding finishing or the like lo to impart a prescribed surface condition. If the maximum equivalent particle diameter d.. of carbides in the surface of the substrate is at most 20 micrometers, abrasive is prevented from falling off of the grinding wheel, and it becomes difficult for grinding scratches to occur. Scratches occurring during grinding finishing and the like have a depth on the order of I - 5 micrometers, and the 15 thickness of the coating is normally on the order of 3 micrometers, so they remain even after surface modification treatment, and they become a source of stress concentrations in the region of contact with the material being rolled or with an opposing roll during rolling, and they become a cause of peeling of the coating. However, in this invention, it is difficult for scratches to occur, so peeling of the 20 coating is also suppressed in this respect.

In this manner, according to this invention, a roll for rolling can be provided which has excellent wear resistance and seizing resistance and which can provide great advances in productivity and great increases in the surface quality of steel plate and which has excellent resistance to accidents and 25 grindability and which also is inexpensive.

(Second Embodiment) [Substrate] A roll for cold rolling according to this invention has a steel substrate.

Specifically, a roll for rolling according to this invention contains C: at least 0.30% and less than 0.60%, Si: at least 0. 15% and less than 0.30%, Mn: 0. 15 - 3.0%, Ni: 0.3 - 3.0%, Cr: 2.0 - 8.0%, and Mo: 0.2 3.0%. Below, the reasons for the limitations on the composition of the substrate will be explained.

5 C: at least 0.30% and less than 0.60% In a ferrous material, C is one of the principal elements having a major effect on various properties, and it is also an important element in this invention.

If the C content is smaller than 0.30%, the hardness necessary for the below described substrate cannot be obtained. On the other hand, if the C content is lo greater than or equal to 0.60%, transformation of the structure and embrittlement of the substrate are promoted, and adhesion between the substrate and the hard coating can no longer be guaranteed. Therefore, in this invention, the C content is defined as at least 0.30% and less than 0.60%. From the same standpoint, the lower limit on the C content is preferably 0.4%.

15 Si: at least 0. 15% and less than 0.30% Si is included as a deoxidizing agent in an amount of at least 0. 15%.

However, if the Si content is greater than or equal to 0.30%, carbides segregate in the form of a chain, and embrittlement is promoted. Therefore, in this invention, the Si content is limited to at least 0. 15% and less than 0.3 0%.

20 Mn: 0. 15 - 3.0% Mn: functions as a deoxidizing agent. In addition, as described below, a substrate according to this invention is normally subjected to high temperature tempering treatment at a temperature of greater than 400'C prior to surface modification treatment, so it contains Mn in order to increase resistance to 25 softening during the high temperature tempering. From this standpoint, at least 0. 15% of Mn is included, but if more than 3.0% is included, the substrate is embrittled. Therefore, in this invention,, the Mn content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the upper limit on the Mn content is preferably at most 2.0%.

Ni: 0.3 - 3.0% Ni is an element which is effective at increasing the toughness of a ferrous material. In particular, in this invention, it has the effect of delaying a change in 5 the structure of the substrate, so it has an important role. Such an effect is exhibited, when the Ni content is at least 0.3%, but if more than 3.0% is included,, the toughness ends up deteriorating. Therefore, in this invention, the Ni content is defined as at least 0.3% and at most 3.0%. From the same standpoint, the lower limit is preferably 0.5% and the upper limit is preferably 2.0%. In io particular, it is more preferable if the upper limit is 1.5%.

Cr: 2.0 - 8.0% Cr is a carbide-forming element. When it is heated to a high-temperature austenite state, it is the element which most readily enters a solid solution. If the Cr content is at least 2.0%, if hardening is carried out from a high temperature of is at least I OOO'C and tempering is carried out at a high temperature exceeding 400'C, secondary hardening becomes marked, and the hardness required of a substrate can beguaranteed. However, if the Cr content exceeds 8.0%, coarse carbides become prominent, the toughness decreases, and the hardness also decreases. Therefore, in this invention, the Cr content is defined as at least 2.0% 2o and at most 8.0%. From the same standpoint, the lower limit is preferably 4.0%, and the upper limit is preferably 6.0%.

Mo: 0.2 - 3.0% Like Cr. Mo is a strong carbide-forming element, and it is an element which exhibits the same or greater effect than Cr on resistance to softening during 25 tempering and precipitation hardening. If the Mo content is less than 0.2%, this effect is small, whereas if it exceeds 3.0%, there is a marked decrease in toughness. Therefore, in this invention, the Mo content is defined as at least 0.2% and at most 3.0%. From the same standpoint, the lower limit is preferably 0.5%, and the upper limit is preferably 2.0%.

In order to increase the hardenability of the substrate, to suppress softening during tempering, to refine carbides, and the like, a substrate of the present invention may if necessary include as optional added elements W: at most 2% 5 and V: less than 0.8%.

In.addition to the above, Fe and unavoidable impurities are present.

In this manner, a substrate according to this invention has a steel composition, so it has excellent grindability and a low cost.

In addition, a substrate according to this invention undergoes tempering treatment at a high temperature (such as a temperature exceeding 400'C) which is higher than the treatment temperature of the below-described surface modification treatment, so it is preferable that the substrate surface and the vicinity thereof be at least a prescribed hardness after tempering treatment from the standpoint of wear resistance. Here, a prescribed hardness means a hardness 15 such that the substrate itself does not undergo plastic deformation even under the action of a heavy load during rolling, or a hardness of the substrate such that indentation marks are not formed in the surface modified roll by foreign matter which comes in during rolling. Specifically, it is HS 70.

[Surface modification treatment, hard coating] 20 A roll for rolling according to this invention undergoes surface modification treatment to form a hard coating on the surface of the substrate.

The hard coating in this invention is formed by the same surface modification treatment as the hard coating in the first embodiment described above, so an explanation will be omitted.

25 A roll for cold rolling according to this invention having such a structure has a substrate composition and particularly a C content, an Si content, and an Ni content which are each optimized, so it is difficult for changes in the structure of the substrate to take place. Therefore, even under severe cold rolling, the adhesion between the substrate and the hard coating can be made adequate and can be maintained over a long period. Therefore, great advances in productivity and great improvements in the surface quality of steel plates can be achieved in cold rolling of steel sheets such as common steel or stainless steel or the like. 5 (Third Embodiment) [Substrate] A roll for rolling according to this invention has a steel substrate.

Specifically, a roll for rolling according to this invention contains C: 0.60 - 3.5%, Si: 0. 15 - 3.0%, N4n: 0. 15 - 3.0%, Mo: 0.5 - 5.0%, and Co: 0.5 - 10%, and the lo ratio of Cr to C (Cr/C) is I - 4. Below, the reasons for the limitations on the composition of the substrate will be explained.

C: 0.60 - 3.5% C is a necessary element both for forming carbides and for guaranteeing the hardness of the matrix. In particular, a substrate according to this invention 15 undergoes tempering treatment at a temperature of greater than 400'C as described below, so in order to guarantee an adequate hardness during the tempering, at least 0.60% is included. If the C content exceeds 3.5%, toughness is remarkably deteriorated. Therefore, in this invention, the C content is defined as at least 0.60% and at most 3.5%. From the same standpoint, the upper limit on 20 the C content is preferably 2.0%, and it is more preferably less than 1.0%. Si: 0. 15 - 3.0% Si is included as a deoxidizing agent. Si is also included because it has the effect of increasing softening resistance during high temperature tempering. From this standpoint, the Si content is at least 0. 15%, but if the Si content 25 exceeds 3.0%, hot workability and toughness decrease. Therefore in this invention, the Si content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the lower limit on the Si content is preferably 1.0%.

Mn: 0. 15 - 3.0% Mn is included for the same objective as Si. Therefore, in this invention, the Mn content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the lower limit on the Mn content is preferably 0.5%, and the upper limit is preferably 2.0%.

5 Mo: 0.5 - 5.0% Mo is included in an amount of at least 0.5% in order to improve resistance to softening during tempering. However, if the Mo content exceeds 5.0%, the toughness of the substrate is deteriorated. Therefore, in this invention, the Mo content is defined as at least 0.5% and at most 5.0%. From the same standpoint, lo the upper limit on the Mo content is preferably 2.0%. Co: 0.5 -10% Co has the effect of delaying aggregation of carbide during high temperature tempering and of suppressing softening, so at least 0.5% is included. However, this effect saturates at a content of 10%, and if the content exceeds this 15 amount, costs are merely increased. Therefore, in this invention, the Co content is defined as at least 0. 5% and at most 10%. From the same standpoint, the upper limit on the Co content is preferably 5%.

Ratio of Cr to C (C&A. -1 - 4 Cr is a carbide-forming element. In this invention, by defining the 2o relationship to the C content as described above, the types of carbides which are formed are controlled. If the (Cr/C) ratio is 4 or below, the carbides which are formed are primarilyM3Ccarbides having a hardness on the order of HV 1000. On the other hand, if the (Cr/C) ratio exceeds 4, harder M7C3 carbides having a hardness on the order of HV 1800 become predominant. Therefore, in the 25 interface of the hard coating and the substrate, the difference in the stifffiess of the carbides in the substrate and the stifffiess of the matrix (matrix hardness: less than HV 1000) becomes large, and the adhesion between the hard coating and the substrate deteriorates. On the other hand, if the (Cr/C) ratio is smaller than 1, hardenability deteriorates, and the hardness of the matrix becomes inadequate. Therefore, in this invention, the (CrIC) ratio is defined as at least I and at most 4. From the same standpoint, the upper limit on the (Cr/C) ratio is preferably 3.

A substrate according to this invention may also contain if necessary as an 5 optional added element V: less than 0.8% in order to increase the hardenability of the substrate, to suppress softening during tempering, to refine carbides, and the like.

In addition to the above, Fe and unavoidable impurities are present.

In this manner, a substrate according to this invention has a steel 1 o composition, so it has excellent grindability- and a low cost.

In addition,, a substrate according to this invention undergoes tempering treatment at a temperature greater than the treatment temperature of the belowdescribed surface modification treatment (such as a temperature exceeding 400'C). It is preferable from the standpoint of wear resistance that the surface of 15 the substrate and the vicinity thereof after tempering treatment have at least a prescribed hardness. Here, a prescribed hardness means a hardness such that the substrate itself does not undergo plastic deformation even under the action of a heavy load during rolling, or a hardness of the substrate such that indentation marks are not formed in the surface modified roll by foreign matter which comes 20 in during rolling. Specifically, it is HS 70.

[Surface modification treatment, hard coating] A roll for rolling according to this invention is one on which surface modification treatment has been carried out to form a hard coating on the surface of a substrate.

A hard coating according to this invention is fonned by the same surface modification treatment as the hard coating in the above-described first embodiment, so an explanation will be omitted.

A roll for cold rolling according to this invention having such a structure optimizes the composition of the substrate, and particularly the ratio (Cr/C) of the C content of the substrate and the Cr content which is determined to be balanced therewith, so carbides are softened. Therefore, the difference between the stiffness of the carbides of the substrate and that of the matrix (matrix hardness:

less than HV 1000) in the interface between the hard coating and the substrate can be suppressed to a small value, so even in cold rolling under severe conditions, the adhesive strength between the substrate and the hard coating can be adequately maintained. Therefore, even during cold rolling of steel sheets such as common steel or stainless steel or the like, great increases in productivity lo and great improvements in the surface quality of steel plates can be achieved.

(Fourth Embodiment) [Substrate] A roll for cold rolling according to this invention has a steel substrate.

Specifically, a roll for rolling according to this invention contains C: at least 0.3 is and I%, Sh at least 0. 15% and at most 3.0%, Mn: 0. 15 3.0%, Cr: 2.0 - 8:0%, Mo: 0.2 - 3.0%, V: 0.05 - 2.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta: 0.01 0.50%. Below, the reasons for the limitations on the composition of the substrate will be explained.

C: at least 0.3% and at most 1.0% 20 C is one of the primary elements which has a marked effect on the various properties of a ferrous material. In this invention as well, it is an important element. If the C content is smaller than 0.3%, the hardness necessary for the substrate as below-described cannot be obtained. On the other hand, if the C content exceeds 1.0%, changes in the structure of the substrate and embrittlement 25 are promoted, and adhesion between the substrate and the hard coating can no longer be guaranteed. Therefore, in this invention, the C content is defined as at least 0.3% and at most 1.0%. From the same standpoint, the lower limit on the C content is preferably 0.4% and the upper limit is preferably 0.6%.

Si: at least 0. 15% and at most 3.0% Si is included in an amount of at least 0. 15% as a deoxidizing agent or in order to increase resistance to softening during high temperature tempering treatment at above 400'C carried out prior to surface modification treatment. If 5 the Si content exceeds 3.0%, hot workability and toughness are decreased.

Therefore, in this invention, the Si content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the upper limit on the Si content is preferably 2.0%.

Mn: 0.15 - 3.0% 10 Mn functions as a deoxidizing agent. Furthermore, as described below, a substrate according to this invention is normally subjected to high temperature tempering treatment at above 400'C prior to surface modification treatment, so Mn is included in order to increase resistance to softening during the high temperature tempering. From this standpoint, Mn is included in an amount of at 15 least 0. 15%, but if the content exceeds 3.0%, hot workability decreases and the substrate is embrittled. Therefore, in this invention, the Mn content is defined as at least 0. 15% and at most 3.0%. From the same standpoint, the upper limit on the Mn content is preferably 2.0%.

Cr: 2.0 - 8.0% 20 Cr is a carbide-forming element. When heating to a high temperature austenite state takes place, it is the element which most easily forms a solid solution in the matrix. If the Cr content is at least 2.0%, if hardening from a high temperature of at least 1000'C is carried out and then tempering at a high temperature of above 400'C is carried out, secondary hardening occurs to a 25 marked degree, and the hardness necessary for a substrate can be guaranteed. However, if the Cr content is greater than 8.0%, coarse carbides become prominent, toughness decreases, and hardness also decreases. Therefore, in this invention, the Cr content is defined as at least 2.0% and at most 8.0%. From the same standpoint, the lower limit is preferably 4.0%, and the upper limit is preferably 6.0%. Mo: 0.2 - 3.0% Like Cr, Mo is a strong carbide-forming element, and it is also an element 5 which has the same or greater effect than Cr on resistance to softening during tempering and precipitation hardening. This effect is small if the Mo content is less than 0.2%, while if it exceeds 3.0%, there is a marked decrease in toughness. Therefore, in this invention, the Mo content is defined as at least 0.2% and at most 3.0%. From the same standpoint, the lower limit is preferably 0.5% and the lo upper limit is preferably 2.0%.

V: 0.05 - 2.0% V is a strong carbide-forming element which combines with C and forins stable carbides. In addition, V forms a solid solution in the matrix less readily than Cr or Mo, and like Mo, it is an element which has a strong effect on wear 1-5 resistance and grindability. In this manner, V is a strong carbide- forming element, so the V content is greatly restricted by the C content. If the V content exceeds 2.0%, the amount of C in the matrix decreases and the desired hardness can no longer be obtained. On the other hand, if the V content is less than 0.05%, the amount of carbides which have excellent wear resistance decreases, so the 20 effect with respect to the various desired properties is markedly decreased. Therefore, in this invention, the V content takes the C content into consideration and is defined as at least 0.05% and at most 2. 0%. From the same standpoint, the lower limit of the V content is preferably 0. 1% and the upper limit is preferably 1.5%.

25 One or more substance selected from the group consisting of Ti, Zr, Nb, and Ta:

0.01-0.50% These elements have an extremely strong affinity for C and N, and they solidify in the form of carbide, nitride, or carbonitride particles. These compounds have the effect of preventing the coarsening of crystal grains during the hardening of the substrate prior to surface modification treatment, and a substrate having fine crystal grains is obtained. In the surface modified roll having this as a substrate, changes in the structure of the substrate surface layer 5 and embrittlement during rolling can be suppressed. In addition, a substrate including these compounds can suppress softening due to tempering of the substrate, so a sufficiently high hardness can be obtained even with high temperature tempering. However, if too much is added, it leads to segregation of these compounds and to a deterioration in mechanical properties and a worsening lo of the grindability of the substrate. Therefore, in this invention, the total amount of at least one substance selected from the group consisting of Ti, Zr, Nb, and Ta is defined as at least 0.01% and at most 0.50%. The lower limit on these elements is preferably 0.05% and the upper limit is preferably 0.30%.

In order to increase the hardenability of the substrate, to suppress softening 15 during tempering, to refine carbides, and the like, a substrate according to this invention may if necessary contain Ni: at most 2.0%, W: at most 2.0%, and Co: at most 5.0% as optional added elements.

In addition to the above, Fe and unavoidable impurities are present.

In this manner, a substrate according to this invention has a steel 20 composition, so it has excellent grindability and a low cost.

In addition, a substrate according to this invention undergoes tempering treatment at a temperature greater than the treatment temperature of the belowdescribed surface modification treatment (such as a temperature exceeding 400'C). It is preferable from the standpoint of wear resistance that the surface of 25 the substrate and the vicinity thereof after tempering treatment have at least a prescribed hardness. Here, a prescribed hardness means a hardness such that the substrate itself does not undergo plastic deformation even under the action of a heavy load during rolling, or a hardness of the substrate such that indentation marks are not formed in the surface modified roll by foreign matter which comes in during rolling. Specifically, it is HS 70. [Surface modification treatment, hard coating] A roll for rolling according to this invention is one on which surface s modification treatment has been carried out to form a hard coating on the surface of a substrate.

A hard coating in this invention is formed by surface modification treatment in the same manner as the hard coating in the above-described first embodiment, so an explanation will be omitted.

10 A roll for cold rolling according to this invention having such a structure has a substrate with a composition which includes a suitable amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta, so it is difficult for changes in the structure of the substrate to take place. Therefore, adhesion between the substrate and the hard coating which is adequate and which is can be maintained for a long period can be obtained even in severe cold rolling.

Therefore, even in cold rolling of steel sheets such as common steel, stainless steel, or the like, great increases in productivity and great improvements in the surface quality of steel plate can be achieved.

(Fifth Embodiment) 20 [Substrate] A roll for cold rolling according to this invention has a steel substrate. Specifically, a roll for rolling according to this invention contains C: at least 0.4% and at most 1.0%, Si: at least 0. 15% and at most 1.0%, Mn: 0. 15 - 1.0%, Cr: 1.0 3.0%, Mo: 0. 15 - 3.0%, V: 0.5 - 5.0%, and Co: 0.5 - 10.0%, and zero stress or a 25 compressive stress is imparted to the surface to be surface modified. Below, the reasons for the limitations on the composition of the substrate and the stress condition of the surface will be explained.

C: at least 0.4% and at most 1.0% C is an element which has a large effect on the hardness of the matrix and on carbide formation. The hardness of the matrix is controlled primarily by the amount of C in solid solution. If the C content is less than 0.4%, the hardness of the matrix is not adequate. On the other hand, if the C content exceeds 1.0%, this 5 leads to solidification of coarse carbides and toughness is deteriorated. Therefore, in this invention, the C content is defined as at least 0.4% and at most 1.0%. From the same standpoint, the lower limit on the C content is preferably 0.6%. S i: at least 0. 15% and at most 1.0% 10 Si is included in an amount of at least 0. 15% as a deoxidizing agent and in order to increase resistance to softening during high temperature tempering treatment at above 400'C carried out prior to surface modification treatment. If the Si content exceeds 1.0%, hot workability and toughness are deteriorated.

Therefore, in this invention, the S i content is defined as at least 0. 15 % and at 15 most 1.0%. From the same standpoint, the upper limit on the Si content is preferably 0.5%.

Mn: 0.15 - 1.0% Mn functions as a deoxidizing agent. Furthermore, as described below, a substrate according to this invention is normally subjected to high temperature 20 tempering treatment at above 400'C prior to surface modification treatment, so Mn is included in order to increase resistance to softening during the high temperature tempering. From this standpoint, Mn is included in an amount of at least 0. 15%, but if the content exceeds 1.0%, hot workability is worsened and the substrate is embrittled. Therefore, in this invention, the Mn content is defined as 25 at least 0. 15% and at most 1.0%. From the same standpoint, the upper limit on the Mn content is preferably 0.5%.

Cr: 1.0 - 3.0% Cr is a carbide-forming element. When heating to a high temperature austenite state takes place, it is the element which most easily forms a solid solution in the matrix. If the Cr content is at least 1.0%, if hardening from a high temperature of at least I OOO'C is carried out and then tempering at a high temperature of above 400'C is carried out, secondary hardening occurs to a 5 marked degree, and the hardness necessary for a substrate can be guaranteed. However, if the Cr content exceeds 3.0%, due to high hardenability, the hardened layer is deep, and the residual stresses after heat treatment are tensile stresses, which induce peeling of the hard coating. Therefore, in this invention, the Cr content is defined as at least 1.0% and at most 3.0%.

lo Mo: 0.15 - 3.0% Like Cr, Mo is a strong carbide-forming element, and it is an element having the same or a stronger effect than Cr with respect to resistance to softening during tempering and precipitation hardening. If the Mo content is less than 0. 15%, such an effect is small, while if it exceeds 3.0%, there is a marked 15 decrease in toughness. Therefore, in this invention, the Mo content is defined as at least 0. 15% and at most 3.0%.

V: 0.5 - 5.0% V is a strong carbide-forming element which combines with C and forms stable carbides. In addition, V forms a solid solution in the matrix less readily 20 than Cr or Mo, and it is an element which like Mo has a strong effect on wear resistance and grindability. In this manner, V is a strong carbide-forming element, so the V content is greatly restricted by the C content. If the V content exceeds 5.0%, the amount of C in the matrix decreases and the desired hardness can no longer be obtained. However, if the V content is less than 0.5%, there is a 25 shortage of granular hard carbides, and the adhesive strength at the interface between the hard coating and the substrate is inadequate. Therefore, in this invention, the V content takes into consideration the C content and is defined as at least 0.5% and at most 5.0%. From the same standpoint, the lower limit on the V content is preferably 1.0%, and the upper limit is preferably 3.0%.

Co: 0.5 - 10.0% Co delays the aggregation of carbides during high temperature tempering and it has the effect of suppressing softening, so it is added in an amount of 0.5%.

5 However, if Co is added in an amount exceeding 10.0%, this effect saturates, and costs merely increase. Therefore, in this invention, the Co content is defined as at least 0.5% and at most 10.0%. From the same standpoint, the lower limit on the Co content is preferably 3.0% and the upper limit is preferably 5.0%.

In addition to the above, Fe and unavoidable impurities are present.

10 It is empirically known that if a tensile stress acts on the surface of a substrate which is subjected to surface modification treatment, the adhesive strength between the coating and the substrate decreases after the treatment.

Therefore, in this invention, the surface residual stresses after heat treatment of a substrate having components adjusted as described above are made zero (a 15 condition in which stresses are not generated) or are made compressive stresses. Even when the surface residual stresses are compressive stresses, if the magnitude thereof is too great, adhesion is reduced, so the surface residual stresses are preferably compressive stresses of at most 500 NTa.

In addition, a substrate according to this invention undergoes tempering treatment at a temperature greater than the treatment temperature of the belowdescribed surface modification treatment (such as a temperature exceeding 400T). It is preferable from the standpoint of wear resistance that the surface of 25 the substrate and the vicinity thereof after tempering treatment have at least a prescribed hardness. Here, a prescribed hardness means a hardness such that the substrate itself does not undergo plastic deformation even under the action of a heavy load during rolling, or a hardness of the substrate such that indentation marks are not formed in the surface modified roll by foreign matter which comes in during rolling. Specifically, it is HS 70. [Surface modification treatment, hard coating] A roll for rolling according to this invention is one on which surface 5 modification treatment has been carried out to form a hard coating on the surface of a substrate.

10 A roll for cold rolling according to this invention having such a structure has a substrate with a composition which includes a suitable amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta, and the surface of the substrate is imparted a zero stress or a compressive stress, so it is difficult for changes in the structure of the substrate to take place. Therefore, is adhesion between the substrate and the hard coating which is adequate and which can be maintained for a long period can be obtained even in severe cold rolling. Therefore, even in cold rolling of steel sheets such as common steel, stainless steel, or the like, great increases in productivity and great improvements in the surface quality of steel plate can be achieved.

20 (Sixth Embodiment) [Substrate] A roll for cold rolling according to this invention has a steel substrate. Specifically, a roll for rolling according to this invention contains C: 0.8 - 1.8%, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 2.0 - 8.0%, Mo: 2.0 - 10.0%, V: 1.0 - 5.0%, 25 Co: at most 10.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta in a total of at most 1.0%. Below, the reasons for the limitations on the composition of the substrate will be explained.

C: at least 0.8% and at most 1.8% C has a large effect on the hardness of the matrix and on carbide formation. The hardness of the matrix is controlled primarily by the amount of C in solid solution. If the C content is less than 0.8%, the hardness necessary for the belowdescribed substrate can no longer be obtained. On the other hand, if the C 5 content exceeds 1.8%, toughness is markedly deteriorated. Therefore, in this invention, the C content is defined as at least 0.8% and at most 1.8%. From the same standpoint, the lower limit on the C content is preferably 1.0% and the upper limit is preferably 1.6%.

Si: at least 0. 15% and at most 3.0% 10 Si is included in an amount of at least 0. 15% as a deoxidizing agent and in order to increase resistance to softening during high temperature tempering treatment at above 400'C carried out prior to surface modification treatment. If the Si content exceeds 3.0%, hot workability and toughness are decreased.

Therefore, in this invention, the Si content is defined as at least 0. 15% and at 1.5 most 3.0%. From the same standpoint, the upper limit on the Si content is preferably 2.0%.

Mn: 0. 15 - 3.0% Mn functions as a deoxidizing agent. Furthermore, as described below, a substrate according to this invention is normally subjected to high temperature 20 tempering treatment at above 400'C prior to surface modification treatment, so Mn is included in order to increase resistance to softening during the high temperature tempering. From this standpoint, Mn is included in an amount of at least 0. 15%, but if the content exceeds 3.0%, the substrate is embrittled. Therefore, in this invention, the Mn content is defined as at least 0. 15% and at 25 most 3.0%. From the same standpoint, the upper limit on the Mn content is preferably 2.0%.

Cr: 2.0 - 8.0% Cr is a carbide-forming element. When heating to a high temperature austenite state takes place, it is the element which most easily forms a solid solution in the matrix. If the Cr content is at least 2.0%, if hardening from a high temperature of at least I OOO'C is carriedout and then tempering at a high temperature of above 400'C is carried out, secondary hardening occurs to a s marked degree, and the hardness necessary for a substrate can be guaranteed. However, if the Cr content is greater than 8.0%, coarse carbides become marked, toughness decreases, and hardness also decreases. Therefore, in this invention, the Cr content is defined as at least 2.0% and at most 8.0%. From the same standpoint, the lower limit is preferably 3.0% and the upper limit is preferably lo 6.0%.

Mo: 2.0 - 10.0% Like Cr, Mo is a strong carbide-forming element, and it is also an element which has the same or greater effect than Cr on resistance to softening during tempering and precipitation hardening. This effect is small if the Mo content is 15 less than 2.0%,, while if it exceeds 10.0%, coarse carbides increase and there is a marked decrease in toughness. Therefore, in this invention, the Mo content is defined as at least 2.0% and at most 10.0% coarse carbides increase. From the same standpoint, the lower limit is preferably 3.0% and the upper limit is preferably 6.0%.

20 V: 1.0 - 5.0% V is a strong carbide-forming element which combines with C and forms stable carbides. In addition, V forms a solid solution in the matrix less readily than Cr or Mo, and it is an element which like Mo has a strong effect on wear resistance and grindability. In this manner, V is a strong carbide- forming 25 element, so the V content is greatly restricted by the C content. If the V content exceeds 5.0%, the amount of C in the matrix decreases and the desired hardness can no longer be obtained. On the other hand, if the V content is less than 1.0%, carbides having excellent wear resistance become scarce, coarse carbides become predominant, and the adhesive strength at the interface of the coating and the substrate becomes inadequate. Therefore, in this invention, the V content takes the C content into consideration and is defined as at least 1.0% and at most 5.0%. From the same standpoint, the lower limit of the V content is preferably 3.0% and 5 the upper limit is preferably 5.0%. Co: at most 10.0% Co delays the aggregation of carbides during high temperature tempering, and it has the effect of suppressing softening, so it is added. However, if Co is added in an amount exceeding 10.0%, this effect saturates and costs merely io increase. Therefore, in this invention, the Co content is defined as at most 10.0%.

From the same standpoint, the upper limit on the Co content is preferably 5.0% and the lower limit is preferably 3.0%.

One or more substance selected from the group consisting of Ti, Zr, Nb, and Ta:

at most 1.0% is These elements have an extremely strong affinity for C and N, and they solidify in the form of carbide, nitride, or carbonitride particles. Much of the solidified material acts as a nucleus at the time of aggregation of eutectic carbides, and it suppresses coarsening of carbides. However, if too much is added, these compounds segregate, leading to a deterioration in mechanical properties and a worsening of the grindability of the substrate. Therefore, in this invention, the total amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta is defined as at most 1.0%. From the same standpoint, the upper limit on these elements is preferably 0.30%, and the lower limit is preferably 0.05%.

25 In order to further suppress softening during tempering of the substrate, a substrate according to this invention may if necessary contain W: at most 10.0% and preferably at most 6.0%.

In addition to the above, Fe and unavoidable impurities are present.

In addition, a substrate according to this invention undergoes tempering treatment at a temperature greater than the treatment temperature of the below5 described surface modification treatment (such as a temperature exceeding 400'C). It is preferable from the standpoint of wear resistance that the surface of the substrate and the vicinity thereof after tempering treatment have at least a prescribed hardness. Here, a prescribed hardness means a hardness such that the substrate itself does not undergo plastic deformation even under the action of a lo heavy load during rolling, or a hardness of the substrate such that indentation marks are not formed in the surface modified roll by foreign matter which comes in during rolling. Specifically, it is HS 70.

[Surface modification treatment, hard coating] A roll for rolling according to this invention is one on which surface 15 modification treatment is carried out to form a hard coating on the surface of a substrate.

20 A roll for cold rolling according to this invention having such a structure has a substrate with a composition which includes a suitable amount of one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta, so it is difficult for changes in the structure of the substrate to take place. Therefore, adhesion between the substrate and the hard coating which is adequate and which 25 can be maintained for a long period can be obtained even in severe cold rolling. Therefore, even in cold rolling of steel sheets such as common steel, stainless steel, or the like, great increases in productivity and great improvements in the surface quality of steel plate can be achieved.

Best Mode For Carrying Out The Invention

The present invention will be described more concretely while referring to examples.

(Example 1)

The nine types shown in Table I as Substrate No. I - Substrate No. 9 underwent hardening, after which they underwent tempering treatment at a higher temperature than a PVD treatment temperature (400'C) to impart a hardness of at least HS 70,, and then they were finished into cylindrical test pieces (30 i o millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was formed by the PVD method. A test evaluating the adhesion of the coating and the substrate was then carried out.

15 Table I

Chemical Composition (wt%) Maximum No.

Equivalent Particle Remarks Diameter of C Si Mn Ni Cr Mo V Co W Carbides ('U M) 1 1. 50 0.30 0.50 0.01 12.00 1.00 0.35 0.01 0.01 35 Conventional (SKD, 1) 2 0. 85 0.30 0. 30 0.01 4.15 5.00 1.95 0.01 6.10 45 Conventional (SKH51) 3 0.70 1.50 1.00 0.01 9.00 1.50 0.50 1.00 0.50 5 4 0.90 2.00 1.50 0.10 6.00 2.00 0.30 2.00 1.00 9 0.80 1.80 1.00 0.50 7.50 1.90 0.15 4.50 0.50 10 Present Invention 6 0.95 2.20 0.50 0.10 5.50 1.00 0.20 1.50 0.50 13 7 1.00 1.00 0.80 0.01 5.00 0.50 0.05 0.70 0.01 15 8 0.85 1.20 1.00 0.20 9.50 0.50 0.01 1.50 0.50 19 9 1.15 1.00 0.70 0.01 8.00 0.50 0.05 0.60 0.10 25 Comparative In the adhesion test, two cylindrical test pieces having the same shape were in rolling and sliding contact. For the opposing test piece, a 0.8%C - 5%Cr forged steel which is a standard steel for a roll for rolling was used, and it was 5 given a hardness of HS 70 by hardening and tempering.

In the test, Hertzian stress was set to 200 MPa. This value corresponds to the maximum surface pressure during actual cold rolling. The slip rate of the two cylinders was 5%, and they were rotated at a rotational speed of 800 rpm using a kerosine lubricant having poor lubricating properties.

10 It was determined whether or not there was peeling of the coating by stopping the test after a suitable number of rotations and by performing magnified observation of the surface condition using a CCD scope.

The test results are compiled into a graph in Figure 1. In the graph of Figure 1, the relationship between the maximum equivalent particle diameter dmax 15 (micrometers) and the number of rotations Ni until breakage is shown.

Substrate No. 1, which was a conventional example of a substrate (SKD 11), Substrate No. 2, which was a conventional example of a substrate (SKD 5 1), and Substrate No. 9, which was a comparative example of a substrate, each had a maximum equivalent particle diameter of carbides which was above the range of 20 the present invention, so each had peeling of a coating formed thereon before the number of rotations of a roll for real cold rolling per use (normally at most 4 x 10 5).

In contrast, Substrate No. 8, which was an example of the present invention having a maximum equivalent particle diameter of carbides of 19 2 5 micrometers, did not have peeling of the coating even when the number of rotations exceeded this number of rotations.

Furthermore, with Substrates Nos. 3 - 7 which had a maximum equivalent particle diameter of at most 15 micrometers, fatigue damage of the substrate was the direct cause of breakage, the adhesive strength of the coating and the substrate was adequate, and peeling of the coating was not a cause of breakage. (Example 2) The twelve types shown in Table 2 as Substrate No. I - Substrate No. 12, 5 underwent hardening, after which they underwent tempering treatment at a higher temperature than a PVD treatment temperature (400'C) to impart a hardness of at least HS 70, and then they were finished into cylindrical test pieces (30 millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was lo formed by the PVD method. A test evaluating the adhesion of the coating and the substrate was then carried out.

Table 2

Chemical Composition (wtYo) No. Remarks C Si Mn Ni Cr Mo V W 1 1.50 0.30 0.50 0.01 12.00 1.00 0.35 0.01 Conventional(SKDID 2 0.85 0.30 0.30 0.01 4.15 5.00 1.90 6.10 Conventional(SKH51) 3 0.45 0.25 0.35 0.23 4.50 1.50 0.01 0.02 Comparative 4 0.50 0.20 0.55 0.55 6.00 0.70 0.01 0.01 Present Invention 0.55 0.25 0.80 0.90 5.00 1.00 0.02 0.01 Present Invention 6 0.45 0.25 1.00 1.20 4.50 0.50 0.02 0.02 Present Invention 7 0.50 0.20 0.50 1.45 4.50 0.70 0.02 0.02 Present Invention 8 0.45 0.15 1.50 1.70 5.50 1.90 0.01 0.03 Present Invention 9 0.55 0.20 0.70 2.70 5.50 1.00 0.02 0.01 Present Invention 0.50 0.25 0.20 3.50 5.00 0.50 0.01 0.02 Comparative 11 0.50 0.45 0.40 1.00 4.00 0.50 0.01 0.02 Comparative 12 0.65 0.25 0.55 1.20. 2.70 0.50 0.02 0.01 Comparative The adhesion evaluation test was carried out in the same manner as in Example 1. The test results of the number of rotations N, until breakage are compiled as a graph in Figure 2.

Substrate No. 1, which was a conventional example of a substrate (SKD 5 11), Substrate No. 2, which was a conventional example of a substrate (SKD 5 1), and Substrates Nos. 3 and 10 - 12, which were comparative examples of substrates, each had peeling of the coatings formed thereon before reaching 2 x 10' rotations of use.

In contrast, Substrates Nos. 4 - 9, which were substrates according to the lo present invention, could be adequately used in actual cold rolling even when the number of rotations of use exceeded 4 x 10' rotations (the normal number of rotations per use of a roll for cold rolling).

(Example 3)

15 The eight types shown in Table 3 as Substrate No. I - Substrate No. 8 underwent hardening, after which they underwent tempering treatment at a higher temperature than a PVD treatment temperature (400'C) to impart a hardness of at least HS 70, and then they were finished into cylindrical test pieces (30 millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra 20 of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was formed by the PVD method. A test evaluating the adhesion of the coating and the substrate was then carried out.

Table 3

Chemical Composition (wt%) T'ype of No. C Si Mh Cr Mo V W Cr/C Carbides Remarks 1 1.50 0.30 0.50 12.00 1.00 0.35 0.01 8.0 M7C3 Conventional(SKDID 2 0.70 1.05 1.50 2.00 1.00 0.01 1.00 2.9 M3C Present Invention 3 0.95 1.50 1.00 2.50 1.50 0.01 1.50 2.6 M3C Present Invention 4 1.80 2.10 0.60 4.50 0.70 0.01 0.70 2.5 M3C Present Invention 5 2.20 1.30 0.55 6.50 1.00 0.02 0.80 3.0 M3C Present Invention 6 3.20 1.00 0.95 8.00 1.80 0.02 4.50 2.5 M3C Present Invention 7 1.15 1.25 0.85 5.20 0.70 0.02 2.00 5.0 M7C3 Comparative 8 3.60 1.10 1.00 10.00 0.80 0.01 1.10 2.8 M3C Comparative The. adhesion evaluation test was carried out in the same manner as in Example I The test results with respect to the number of rotations N2 until 1,5 peeling of the coating are compiled as a graph in Figure 3.

Substrate No. 1, which was a conventional example of a substrate (SKD 11), and Substrate No. 7 and Substrate No. 8, which were comparative examples of substrates, each had peeling of the coating formed thereon before reaching 2 x 10' rotations.

20 In contrast, Substrates Nos. 2 - 6, which were examples of the substrate according to the present invention, could each be adequately used in actual cold rolling even when the number of rotations exceeded 4 x 10' (the normal number of rotations per use by a roll for cold rolling).

(Example 4)

25 The eighteen types shown in Table 4 as Substrate No. I - Substrate No. 18 underwent hardening, after which they underwent tempering treatment at a higher temperature than a PVD treatment temperature (400'Q to impart a hardness of at least HS 70, and then they were finished into cylindrical test pieces (30 millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was formed by the PVD method. A test evaluating the adhesion of the coating and the substrate was then carried out.

Table 4

No. Chemical Composition (Wt%) C S! Mn Ni Cr Mo V w Co Ti Zr Nb Ta Ti+Zr Remarks +Nb+Ta 1 1.50 0.30 0. 0 0.01 12.00 1.00 0.35 0.01 0.01 0.00 0.00 0.00 0.00 0. 00 Conventional Substrate(SKDIO 2 0.85 0.30 0.30 0.01 4.15 5.00 1.90 6.10 0.01 0.00 0.00 0.00 0.00 0. 00 Conventional Substrate(SKI-151) 3 0.55 1.70 0.55 0.01 4.00 0.75 1.00 0.50 0.01 0.00 0.00 0.10 0.10 0. 20 Present Invention Substrate 4 0.52 2.70 0.70 1.00 5.25 2.55 0.45 0.50 0.01 0.05 0.10 0.00 0.00 0. 15 Present Invention Substrate 0.90 0.85 1.70 0.50 4.85 1.25 0.10 0.01 5.00 0.00 0.00 0.01 0.00 0. 01 Present Invention Substrate 6 0.45 0.55 0.15 0.01 2.50 1.00 1.70 0.01 0.01 0.10 0.00 0.00 0.00 0. 10 Present Invention Substrate 7 0.50 0.15 1.25 0.01 5.80 2.00 0.35 1.00 0.01 0.10 0.10 0.20 0.05 0. 45 Present Invention Substrate 8 0.35 0.45 2.70 1.70 4.25 0.35 0.75 0.50 3.50 0.00 0.05 0.00 0.00 0. 05 Present Invention Substrate 9 0.48 0.35 0.45 0.01 6.00 1.40 0.05 0.01 0.01 0.00 0.05 0.10 0.05 0. 20 Present Invention Substrate 0.60 0.70 2.20 0.01 7.50 0.50 1.45 0.01 0.01 0.05 0.10 0.05 0.05 0.25 Present Invention Substrate 11 0.75 1.25 0.85 0.50 5.10 1.85 1.10 1.70 0.01 0.10 0.00 0.20 0.05 0.35 Present Invention Substrate 12 0.40 2.20 0.35 0.50 5.50 1.05 0.50 0.01 4.00 0.00 0.10 0.05 0.00 0.15 Present Invention Substrate 13 0.50 0.70 1.60 0.01 4.75 1. 10 0.35 1.00 0.01 0.00 0.00 0. 00 0.00 0. 00 Comparative Substrate Regarding Ti+Zr+Nb+Ta 14 0.60 1.60 0.55 0.01 5.85 0.55 0.25 0.01 0.01 0.10 0.25 0.15 0.05 0.55 Comparative Substrate Regarding Ti+Zr+Nb+Ta 0.55 0.35 0.45 0.50 4.95 1.20 1.10 0.01 4.50 0.20 0.20 0.20 0.05 0.65 Comparative Substrate Regarding TI+Zr+Nb+Ta 16 0.40 0.55 0.70 0.01 5.20 1.75 0.45 0.01 0.01 0.05 0.30 0.15 0.10 0.60 Comparative Substrate Regarding Ti+Zr+Nb+Ta 17 0.45 1.20 0.35 0.50 5.45 0.95 1.50 0.50 0.01 0.00 0.15 0.25 0.15 0.55 Comparative Substrate Regarding Ti+Zr+Nb+Ta 18 1.05 0.45 1.20 0.01 4.20 1.45 0.85 0.01 0.01 0.10 0.00 0.10 0.00 0. 20 Comparative Substrate Regarding C I w IF The adhesion evaluation test was carried out in the same manner as in Example 1. The test results with respect to the number of rotations N2until peeling of the coating are compiled as a graph in Figure 4.

Substrate No. 1, which was a conventional example of a substrate, 5 Substrate No. 2, which was a conventional example of a substrate, and Substrates Nos. 13 - 18, which were comparative examples of substrates, each had peeling of the coating formed thereon before reaching 2 x 10' rotations of use.

In contrast, Substrates Nos. 3 - 12, which were examples of the substrate according to the present invention, could be adequately used in actual cold rolling 1 o even when the number of rotations exceeded 4 x 10' (the normal number of rotations per use by a roll for real cold rolling).

(Example 5)

The twelve types shown in Table 5 as Substrate No. I - Substrate No. 12 underwent hardening, after which they underwent tempering treatment at a higher 15 temperature than a PVD treatment temperature (400'C) to impart a hardness of at least HS 70, and then they were finished into cylindrical test pieces (30 millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was formed by the PVD method. A test evaluating the adhesion of the coating and 20 the substrate was then carried out. In this example, the surface stress was adjusted by the hardening conditions of the heating temperature and the cooling speed, and by sub-zero treatment.

Table 5

Chemical Composition (wt%) Surface No. Remarks Stress C Si Mn Cr Mo V Co (MPa) 1 1.50 0.30 0.50 12.00 1.00 0.35 0.01 50 Conventional Substrate(SKDII) 2 0.75 0.35 0.40 1.50 0.45 1.50 3.50 -100 Present Invention Substrate 3 0.60 0.40 0.65 2.75 0.55 0.55 1.00 -50 Present Invention Substrate 4 0.85 0.85 0.35 2.00 0.40 2.00 4.50 -450 Present Invention Substrate 5 0.95 0.30 0.20 1.20 0.20 2.25 3.75 -250 Present Invention Substrate 6 0.45 0.65 0.15 2.50 2.50 4.50 2.50 -50 Present Invention Substrate 7 0.80 0.25 0.20 1.80 1.50 3.00 8.00 - 100 Present Invention Substrate 8 0.65 0.15 0.75 2.25 0.50 0.85 3.35 - 10 Present Invention Substrate 9 0.75 0.30 0.40 2.05 2.65 1.05 3.15 20 Comparative Substrate Regarding Surface Stress 10 0.85 0.45 0.40 1.50 0.55 2.30 4.50 -600 Comparative Substrate Regarding Surface Stress 11 0.75 0.35 0.35 3.50 2.00 1.15 3.35 20 Comparative Substrate Regarding Surface Stress and Cr Content 18 1.05 0 ' 40 0.25 1.80 0.45 2.00 3.85 -150 Compar ative Substrate Regarding C The adhesion evaluation test was carried out in the same manner as in Example 1. The test results with respect to the number of rotations N, until peeling of the coating are compiled as a graph in Figure 5.

20 Substrate No. I which was a conventional example of a substrate, Substrates Nos. 9, 11, and 12, which were comparative examples of substrates, and Substrate No. 10, which was a conventional example of a substrate having an extremely large compressive stress, each had peeling of the coating formed thereon before reaching 4 x 10' rotations of use.

25 In contrast, Substrates Nos. 2 - 8, which were examples of the substrate according to the present invention, could be,adequately used in actual cold rolling even when the number of rotations exceeded 4 x 105 (the normal number of rotations per use by a roll for cold rolling).

(Example 6)

The eighteen types shown in Table I as Substrate No. I - Substrate No. 18 underwent hardening, after which they underwent tempering treatment at a higher temperature than a PVD treatment temperature (400'C) to impart a hardness of at 5 least HS 70, and then they were finished into cylindrical test pieces (30 millimeters in diameter, 8 millimeters wide) having a surface with a roughness Ra of 0. 1 micrometers. Then, a TiN coating with a thickness of 3 micrometers was formed by the PVD method. A test evaluating the adhesion of the coating and the substrate was then carried out. In this example, the surface stress was 1 o adjusted by the hardening conditions of the heating temperature and the cooling speed, and by sub-zero treatment.

Table 6

No. Chemical Composition (wt%) C Si Mn Cr MO V w Co T! Zr Nb Ta Ti+Zr Remarks +Nb+Ta 1 1.50 0.30 0.50 12.00 1.00 0.35 0.01 0.01 0.00 0.00 0.00 0.00 0. 00 Conventional Substrate(SKDID 2 0.85 0.30 0.30 4.15 5.00 1.90 6.10 0.01 0.00 0.00 0.00 0.00 0. 00 Conventional Substrate(SKH51) 3 1.35 1.70 0.55 4.00 4.00 3.30 1.75 4. 10 0. 10 0.05 0. 10 0.05 0. 30 Present Invention Substrate 4 1.05 2.70 0.70 5.25 3.30 1.50 7.50 1. 10 0.00 0.00 0.50 0.35 0. 85 Present Invention Substrate 5 1.55 0.85 1.70 4.85 5.25 4.20 3.00 9.00 0.00 0.00 0.05 0.00 0. 05 Present Invention Substrate 6 1.30 0.55 0. 15 2.50 2.50 3.80 9.20 4.90 0. 10 0.00 0. 15 0.00 0. 25 Present Invention Substrate 7 0.85 0. 15 1.25 5.80 3.80 4. 10 4.00 5.00 0. 15 0.00 0.00 0.00 0. 15 Present Invention Substrate 8 1.40 0.45 2.70 4.25 4.50 3.00 1.25 4.85 0.10 0.10 0.25 0.15 0. 60 Present Invention Substrate 9 1.15 0.35 0.45 6.00 5.50 3.10 0.01 3.75 0.10 0.10 0.00 0.00 0. 20 Present Invention Substrate 10 1.30 0.55 0.35 5.00 9.50 4.90 1.50 7.50 0.00 0.25 0. 10 0.00 0. 35 Present Invention Substrate 11 1.20 0.70 2.20 7.50 6.00 2.50 2.80 0.95 0.05 0.05 0.20 0.10 0. 40 Present Invention Substrate 12 1.75 1.25 0.85 5.10 7.00 3.50 0.01 4.50 0.00 0.00 0.10 0.20 0. 30 Present Invention Substrate 13 1.25 2.20 0.35 5.50 4.85 3.75 1.30 4.00 0.00 0.10 0.00 0.00 0. 10 Present Invention Substrate 14 1.25 0.70 1.60 4.75 4.75 3.80 1. 55 4.85 0. 10 0.50 0.30 0.20 1. 10 Comparative Substrate Regarding Ti+Zr+Nb+Ta 15 1. 15 0.35 0.45 4.95 3.50 4.00 3.00 4.50 0.30 0.20 0.50 0.20 1. 20 Comparative Substrate Regarding Ti+Zr+Nb+Ta 16 1.40 0.55 0.70 5.20 5.80 4.70 0.01 5.00 0.40 0.00 0.50 0.15 1. 05 Comparative Substrate Regarding Ti+Zr+Nb+Ta 17 1.35 1.20 0.35 5.45 5.35 3.20 1.65 4.75 0.00 0.40 0.35 0.40 1. 15 Comparative Substrate Regarding TI+ZrfNb+Ta 18 1.90 0.45 1.20 4.20 4.00 3.90 1.05 4.15 0.10 0.05 0.10 0.00 0. 25 Comparative Substrate I Regarding C 1 -4, lio The adhesion evaluation test was carried out in the same manner as in Example 1. The test results with respect to the number of rotations N2 until peeling of the coating are compiled as a graph in Figure 6.

Substrates Nos. I and 2, which were conventional examples of a substrate, 5 and Substrates Nos. 14 - 18, which were comparative examples of a substrate, each had. peeling of a coating formed thereon before reaching 2 x 10' rotations.

In contrast, Substrates nos. 3 - 13, which were examples of the present invention, were each adequate for use in actual cold rolling each when the number of rotations of use exceeded 4 x 10' (the usual number of rotations per lo use of a roll for cold rolling).

Possibility of Industrial Use In the present invention, in a roll for rolling in which a steel substrate has undergone surface modification treatment, 15 the adhesion between a coating and the substrate can be increased by improvements of the substrate, and as a result, a roll for rolling can be provided which does not have peeling of a hard coating even during rolling operation under severe conditions and which can be stably used for long periods and which has excellent wear resistance,, seizing resistance, resistance to accidents, and 20 grindability, and which also has a low cost.

Accordingly, a roll for rolling according to the present invention can provide great increases in productivity and great improvements in the surface quality of steel plate by applying a roll for rolling according to the present invention to cold rolling of steel sheet such as common steel, stainless steel, or 2S the like.

The significance of the present invention which has such effects is extremely great.

Claims

1. A roll for rolling comprising a steel substrate and a hard coating formed on the surface of the substrate by surface modification treatment, characterized in that the maximum equivalent particle diameter of carbides dispersed on the surface of the substrate is at most 20 micrometers.

2. A roll for rolling as claimed in claim I wherein the substrate contains, in mass %, C: 0.60 - 1. 1 %, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 3.0 - 12.0%, lo Mo: 0.5 - 5.0%, and Co: 0.5 - 10%.

3. A roll for cold rolling characterized by comprising a steel substrate containing, in mass %, C: at least 0.3 0% and less than 0.60%, Si: at least 0. 15% and less than 0.30%, Mn: 0. 15 - 3.0%, Ni: 0.3 - 3.0%, Cr: 2. 0 - 8.0%, and Mo:

1-5 0.2 - IM, and a hard coating forined on the surface of the substrate by surface modification treatment.

4. A roll for rolling characterized by comprising a steel substrate containing, in mass %, C: 0.60 - 3.5%, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Mo:

20 0.5-5.0%,Co:0.5-10%,witharatioofCrtoC(Cr/C)ofl-4,andahard coating formed on the surface of the substrate by surface modification treatment.

5. A roll for rolling characterized by comprising a steel substrate containing, in mass %, C: 0.3 - 1.0%, Si: 0. 15 - 3.0%, Mn: 0. 15 - 3.0%, Cr: 2.0 2-5 -8.0%, Mo: 0.2 - 3.0%, V: 0.05 - 2.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta in a total amount 0.01 - 0.50%, and a hard coating formed on the surface of the substrate by surface modification treatment.

6. A roll for rolling characterized by comprising a steel substrate containing, in mass %, C: 0.4 - 1.0%, Si: 0. 15 - 1.0%, Mn: 0. 15 - 1.0%, Cr: 1.0 - 3.0%, Mo: 0. 15 - 3.0%, V: 0.5 - 5.0%, and Co: 0.50 - 10.0%, with zero stress or a compressive stress being imparted to the surface to be surface modified, and 5 a hard coating formed on the surface of the substrate by surface modification treatment.

7. A roll for rolling characterized by comprising a steel substrate containing, in mass %, C: 0.8 - 1.8%, Si: 0. 15 - 3.0%, Mn: 0. 15 -3.0%,, Cr: 2.0 - lo8.0%, Mo: 2.0 - 10.0%, V: 1.0 - 5.0%, Co: at most 10.0%, and one or more substance selected from the group consisting of Ti, Zr, Nb, and Ta in a total amount of at most 1.0%, and a hard coating formed on the surface of the substrate by surface modification treatment.

15

8. A roll for rolling as claimed in any one of claims I - 7 wherein the surface modification treatment is carried out by the PVD method or the CVD method.