JP6558207B2 - Roll for metal plate rolling - Google Patents

Description

  The present invention relates to a roll for rolling metal sheets.

  For cold rolling of a metal plate where surface quality is important, a small-diameter work roll having a diameter of 150 mm or less, which is relatively easy to control the load during rolling, is used. For this work roll material, steel materials such as die steel and high-speed steel whose surface hardness is increased by heat treatment are frequently used.

  Patent Document 1 describes a technique of providing a hard ceramic film layer such as TiN on the surface of a work roll in order to improve wear resistance.

JP-A-4-253511

  When rolling a metal plate repeatedly with a work roll, an adherent may adhere to the roll surface. Such unevenness of the adherend is transferred to the material to be rolled and becomes a surface defect of the material to be rolled, so that the surface quality is deteriorated. Such a problem becomes apparent in applications where high surface properties are required. In addition, since the adherend on the surface of the work roll is also transferred to the intermediate roll or the backup roll, it is necessary to clean or replace these rolls, which may significantly impair the productivity. For this reason, it is necessary to prevent adhesion of the adherend to the roll surface.

  As a result of examining the surface of the work roll used for rolling a pure nickel metal plate in detail, the present inventors have found that most of the adhered products are mainly composed of nickel. That is, it has been found that the cause of the adherend is mainly a component in the material to be rolled. And while there are few these deposits, it does not become a problem in particular, However, The said problem becomes obvious when the adhesion thing becomes large gradually. As a coping method, if the rolling reduction during rolling is reduced, the amount of elements contained in the material to be rolled can be reduced on the roll surface, and the problem of deterioration of the surface properties due to adhesives is less likely to occur. . However, the number of rolling passes increases and production efficiency is inevitably lowered.

  The above mechanism is not limited to the rolling roll of pure nickel metal plate, but is the same for the rolling roll of pure titanium metal plate and titanium alloy plate. The main component of the adherend formed on the work roll is titanium. there were.

  In Patent Document 1, no consideration is given to prevention of adhesion of adherents.

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to provide a roll for rolling a metal plate that can prevent adhesion of the work roll surface.

  The inventors divided a work roll (forged steel, no surface treatment) used for rolling a pure nickel plate, and analyzed the surface state with a SEM-EDS apparatus. As shown in FIG. 1, this work roll is a 6-stage mill work roll 4 configured with an intermediate roll 2 and a backup roll 3. In the 6-stage mill, the workpiece 1 of a pure nickel plate is rolled by passing between a pair of work rolls 4 and 4 installed at a predetermined interval. As shown in FIG. 2, the work roll 4 includes, for example, a roll part 4a at the center, a small diameter part 4b at both outer sides thereof, and a large diameter part 4c at both ends, and a work (not shown) at the central part of the roll part 4a. There is a sliding portion 4d. As a result of observing the test material obtained by cutting the rolling center portion, the rolling end portion, and the like with respect to the sliding portion 4d, the present inventors have found that a Ni adherend is attached to the roll surface, and the surface layer of the adherend Fe and Cr were also observed. Depending on the position of the roll in the barrel direction, an agglomerated material having a maximum thickness of about 5 μm was observed.

  Therefore, it was found that the adherend adhered to the work roll surface was Ni of the material to be rolled. Moreover, about the observed Fe and Cr, it is estimated that the component derived from the backup roll or the intermediate roll is transferred to the work roll.

  That is, there is a possibility that the backup roll or the intermediate roll is worn under the sliding condition, and the wear powder is transferred to the work roll and aggregates and adheres on the work roll surface. The production line is not only cold-rolled with a pure nickel plate but also cold-rolled with a SUS steel plate or the like. At this time, the work roll is changed depending on the type of the material to be rolled, but common parts such as the intermediate roll and the backup roll are not changed. For this reason, when a SUS steel plate or the like is cold-rolled before cold rolling of a pure nickel plate, elements such as Fe and Cr derived from the SUS steel plate remain in a rolling device such as an intermediate roll and a backup roll. May be transferred to the work roll and aggregated and adhered on the work roll surface.

  On the other hand, according to the technique described in Patent Document 1, the present inventors formed a TiN layer on the surface of the work roll and rolled the pure nickel metal plate, and the work roll used for rolling was the same as described above. When the surface state was analyzed with a SEM-EDS apparatus, adhesion of nickel to the work roll was confirmed. This is because TiN has high hardness and is excellent in terms of wear resistance, but the friction coefficient is as high as 0.6 to 0.8, and the component derived from the material to be rolled adheres during rolling (sliding). It is thought that. For this reason, in order to maintain the surface properties of the material to be rolled, reduction of rolling load, reduction of rolling speed, etc. are unavoidable, and deterioration of production efficiency is inevitable.

  In addition, Ni of a to-be-rolled material has chemical affinity with the Ti particle | grains which comprise TiN also at room temperature vicinity, It is thought that it is especially easy to adhere.

  Accordingly, the present inventors have studied a surface treatment method that has high hardness, sufficient durability, a low friction coefficient, and that does not cause adhesion of components derived from the material to be rolled. We focused on like carbon (hereinafter referred to as “DLC”). DLC is an amorphous material in which diamond bonds and graphite bonds are mixed. Since DLC has an amorphous structure, it has no crystal grain boundaries and has a very smooth surface compared to a hard film such as TiN. And although the friction coefficient of DLC is based also on a diamond bond / graphite bond ratio, even if it is high, it is 0.15 or less, and is far lower than the conventional hard protective film represented by TiN. In particular, nickel and DLC are considered to be a major reason that they are chemically incompatible.

By the way, the medium carbon steel used for the roll base has a linear thermal expansion coefficient (hereinafter referred to as “β”) of about 10 to 11 × 10 ⁻⁶ / ° C., whereas DLC β is 1.0-2.0 × 10 ⁻⁶ / ° C., which is a big difference. For this reason, when the DLC is directly coated on the surface of the roll base, internal residual stress exists at the bonding interface. That is, tensile stress is applied to the DLC coating layer side, and compressive stress is applied to the roll base material side. Accordingly, the DLC coating layer may be peeled off from the roll base material. When peeling of the DLC coating layer occurs, the surface properties of the material to be rolled are deteriorated. For this reason, it is necessary to reinforce the adhesion between the DLC coating layer and the roll base material.

  Therefore, the present inventors studied to incorporate a hard protective film having β in the intermediate zone between the DLC coating layer and the roll base material as an intermediate layer at the interface between the DLC and the roll base material. When the present inventors measured the adhesion when the DLC is directly coated on the surface of the roll base material, it is only 30 N at the maximum. However, silicon carbide (β = 3.7), titanium carbide (8.0), chromium (4.9), silicon (3.0), and niobium (7.0) are applied as the intermediate layer. In this case, the tendency of increasing the contact force to 40 N at least was confirmed.

  The following is inferred as a mechanism by which the above-mentioned adhesion strength has greatly increased. That is, by providing an intermediate layer in which β is in the intermediate zone between the DLC coating layer and the roll substrate, excessive internal residual stress does not occur as in the case where DLC is directly coated on the surface of the roll substrate. The internal residual stress at each bonding interface of the intermediate layer / roll substrate is relatively small. Although it is theoretically impossible to completely eliminate internal residual stress, the threshold value of adhesion force leading to DLC peeling is reduced by keeping the load relatively small and further distributing the load stepwise within the multilayer structure. Presumed to be higher.

  Furthermore, when silicon carbide or titanium carbide is applied as the intermediate layer, it is possible to have affinity at the bonding interface between both DLC having carbon as a main constituent element and a roll base material having a predetermined carbon concentration. Become. Here, affinity means a chemical bond resulting from the covalent bond of carbon. Further, pure metals such as chromium, silicon and niobium easily form a compound of metal carbide, and form an adhesion strengthening layer composed of a metal carbide thin film layer at the bonding interface.

  This invention is made | formed based on said knowledge, and makes a summary the following roll for metal plate rolling.

  (1) A roll used to roll a metal plate containing at least one selected from Ni, Ti and Cr, and a diamond base having an amorphous structure in which a roll base material, diamond bonds and graphite bonds are mixed A roll for rolling a metal plate, comprising: a carbon coating layer; and an intermediate layer made of a metal carbide or pure metal formed at an adhesive interface between the roll base material and the diamond-like carbon coating layer.

  (2) The roll for rolling a metal sheet according to (1), wherein a friction coefficient of the surface of the diamond like carbon coating layer is 0.15 or less.

  (3) The metal plate rolling roll according to (1) or (2), wherein the diamond-like carbon coating layer has a thickness of 1 to 10 μm.

  (4) The diamond like carbon coating layer is a crystal ratio of a carbon compound having a diamond type crystal structure and a carbon compound having a graphite type crystal structure, and a ratio of the carbon compound having the diamond type crystal structure is 60 to 80%. A roll for rolling metal sheets according to any one of (1) to (3).

  (5) The roll for metal plate rolling according to any one of (1) to (4), which is a roll used to roll a metal plate, containing 99.5% by mass or more of Ni or Ti.

  (6) The roll for metal sheet rolling according to any one of (1) to (5), wherein the intermediate layer is made of one or more selected from silicon carbide, titanium carbide, Cr, Si and Nb.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to prevent adhesion of the work roll surface, peeling of the DLC coating layer formed in the work roll surface can be prevented effectively. For this reason, the roll for metal plate rolling of this invention can maintain the surface property of a to-be-rolled material for a long time.

The figure which shows the example of an apparatus structure of a 6-stage mill. The figure which shows the example of a work roll. Sectional drawing which shows the example of the work roll of this invention. Sectional photograph (scanning electron microscope image) of the work roll of Comparative Example 3. The photograph which shows the surface state of the work roll and rolled material in an Example. (a) Surface state of the work roll of Comparative Example 1, (b) Surface state of the work roll of Comparative Example 3, and (c) Surface state of the material to be rolled rolled using the work roll of Comparative Example 3.

  The present invention relates to a roll used for rolling a metal plate, which contains one or more selected from Ni, Ti and Cr. The roll of the present invention can prevent such adhesion even when a metal plate containing an element that easily adheres to the roll surface is rolled. Examples of the metal plate containing one or more selected from Ni, Ti and Cr include 99.5% by mass or more of pure Ni, 99.5% by mass or more of pure Ti, Ti alloy, and stainless steel. It is done. The present invention can be applied to all rolls related to rolling, such as the intermediate roll 2 and the backup roll 3, in addition to the work roll 1 shown in FIG. However, it is preferable to apply to the work roll 1 in direct contact with the material to be rolled (work).

  As shown in FIG. 3, the roll 4 for metal sheet rolling of the present invention includes a diamond-like carbon coating layer 40 on the surface of the roll portion 4a. That is, the roll part 4 a is composed of a diamond like carbon coating layer 40 and a base part 41, and includes an intermediate layer 42 at the interface between the diamond like carbon coating layer 40 and the base part 41. The diamond-like carbon (DLC) coating layer 40 has an amorphous structure in which diamond bonds (cubic crystals, sp3 bonds) and graphite bonds (hexagonal crystals, sp2 bonds) are mixed. For this reason, DLC has a high hardness similar to that of cemented carbide, and has a low friction coefficient at each stage as compared with a metal oxide film such as alumina, a metal carbide film such as TiC, and a metal nitride film such as TiN. High lubricity. In particular, it is preferable to use a DLC coating layer having a composition of ta-C: H type (hydrogenated tetrahedral amorphous carbon).

  The friction coefficient on the surface of the diamond-like carbon coating layer is preferably 0.2 or less in order to prevent adhesion of Ni, Ti, Cr and the like. More preferred is 0.15 or less, and further preferred is 0.1 or less.

  The composition of the DLC coating layer is not particularly limited. Therefore, the ratio of the graphite bond abundance sp2 and the diamond bond abundance sp3 (sp3 / sp2) may be 0.60 to 0.80 in terms of crystal ratio.

  The thickness of the DLC coating layer is preferably 1 μm or more in order to ensure the function as a hard protective film. On the other hand, if the DLC coating layer is too thick, the tensile stress applied to the interface between the DLC coating layer and the base material portion becomes too strong based on the “lever principle”, and the DLC coating layer is removed from the base material portion. May peel off. Such a situation is likely to occur particularly when the shear stress during rolling exceeds a predetermined value, such as in high-load rolling. For this reason, it is preferable that the thickness of a DLC coating layer shall be 10 micrometers or less.

  The high lubricity of DLC can be quantitatively grasped by using a low coefficient of friction as an index. And because of the low coefficient of friction, the graphite that constitutes DLC has a tortoiseshell-like layered structure and exhibits extremely strong bonds (covalent bonds, also referred to as σ bonds) in the same layer, while the interlayer (tortoiseshell) In the upper and lower surfaces, the bond remains weak (Van der Waals force, also called π bond). For this reason, when the latter bonding force is less than the shear stress applied to the DLC surface, a slip phenomenon between layers (slip on the order of several Å) occurs relatively easily, and the bond is dissociated. As a result, high lubricity of the DLC coating film layer can be obtained.

  Then, since shear stress always acts on the work roll surface during rolling, the DLC is worn, and the DLC does not peel off even in a rolling environment, and the film must be formed under the remaining conditions. If the lower limit value of the film forming conditions is a DLC thickness of 1 μm or more, at least the intended production process (rolling total length of the steel sheet) can be processed.

  In addition, the thickness of a DLC coating layer can be adjusted with the time which exposes the base-material part of a roll in the film-forming apparatus. Here, for example, when the DLC film is formed on the base material portion using the physical vapor deposition method (PVD method), the film forming temperature may exceed the tempering temperature of the steel material constituting the base material portion. Even if the film formation temperature exceeds the tempering temperature, there is no particular problem if the film formation time is short. However, if the film formation time is too long, the steel material constituting the base material part of the roll will be inside the film formation apparatus. There is a risk of unexpected softening as a result of tempering. In this respect, if the thickness of the DLC coating layer is 10 μm or less, the film can be formed in a relatively short time, so even if the film forming temperature is high, the influence on the base material of the roll should be made small enough to be ignored. Can do. Moreover, since the DLC coating layer has a low heat-resistant temperature, the roll of the present invention is not suitable for hot rolling, but is suitable for warm rolling or cold rolling.

  The DLC coating layer is formed directly or via a buffer film on the surface of the base of the roll using a dry film forming method such as chemical vapor deposition (CVD) or physical vapor deposition (PVD). Can do. With the recent development of film forming apparatus technology, in addition to an ultra-high hardness film with a controlled hydrogen content, a hard film in which chromium, silicon, etc. are incorporated into a matrix as hard particles has been put into practical use. The processing conditions of the PVD method or the CVD method may be in accordance with well-known and conventional conditions as long as the steel material structure after the heat treatment of the steel material constituting the base portion of the roll and the steel material structure are not impaired. It is not limited. For example, an arc ion plating method is preferable for PVD, and a plasma CVD method is preferable for CVD in order to form a DLC film uniformly and uniformly on the entire surface of the roll circumference.

  The chemical composition of the base material is not particularly limited as long as it has a predetermined mechanical performance (surface hardness: 800 or more in Hv, surface roughness: about 0.06 in Ra). In the standard, SKD series, SKH series and the like are listed as the steel material classification.

The intermediate layer is made of metal carbide or pure metal. By forming such an intermediate layer at the adhesive interface between the roll base material and the diamond like carbon coating layer, it becomes possible to reinforce the adhesion between the DLC coating layer and the roll base material. In particular, it is preferable to provide a hard protective film having β in the intermediate zone of the DLC coating layer and the roll substrate as the intermediate layer. Incidentally, the carbon steel β in used for the roll base is about 10~11 × ^{10 -6} / ℃, the β of DLC, which is 1.0~2.0 × ^{10 -6} / ℃. Accordingly, silicon carbide (β = 3.7), titanium carbide (8.0), chromium (4.9), silicon (3.0), and niobium (7.0) are provided as intermediate layers. It is preferable.

  This makes it possible to relieve internal residual stress that occurs at the adhesive interface when the DLC is directly coated on the surface of the roll substrate. In particular, when one or more of silicon carbide and titanium carbide is applied as the intermediate layer, affinity should be given at the bonding interface between both DLC containing carbon as a main constituent element and a roll base material containing a predetermined carbon concentration. Is possible. Here, affinity means a chemical bond resulting from the covalent bond of carbon. On the other hand, chromium, silicon and niobium, which are pure metals, easily form metal carbides and form an adhesion strengthening layer composed of a metal carbide thin film layer at the bonding interface.

  First, in order to confirm the effect when the DLC coating layer is formed, the DLC coating layer is formed on the surface of the forged steel work roll (Comparative Example 1), the super steel work roll (Comparative Example 2), and the forged steel base material part. A prepared work roll (Comparative Example 3) is prepared, and a pure nickel foil (plate thickness 0.2 mm, plate width 600 mm, nickel purity ≧ 99.5%) is used as a material to be rolled in a 6-stage mill shown in FIG. The sheet was rolled to a thickness of 0.1 mm (pass number: 1 pass, rolling load: 70 to 80 ton total rolling length: 10,000 m), and the surface properties of the material to be rolled were confirmed. In addition, the shape of the work roll was the shape shown in FIG. 2, the body length of the roll part was 1,000 mm, and the diameter of the roll part was 80 mm.

  In the work roll of Comparative Example 3, the surface of the work roll made of forged steel is placed in a plasma CVD film forming apparatus to form a DLC coating layer having a composition of ta-C: H type (hydrogenated tetrahedral amorphous carbon). Filmed. The film thickness of this DLC coating layer was 1.3 μm. The ratio (sp3 / sp2) was 75%. As shown in FIG. 4, a uniform DLC coating layer was formed on the surface of the work roll of Comparative Example 3.

  As shown in FIG. 5, the adhesion is noticeable in the forged steel work roll of Comparative Example 1 (see FIG. 5 (a)), but the adhesion is not confirmed in the DLC-coated forged steel work roll of Comparative Example 3 (FIG. 5 ( b)), and no surface defects occurred in the rolled pure nickel foil (see FIG. 5 (c)).

  Next, an experiment was conducted to confirm the effect when the intermediate layer shown in Table 1 was provided between the DLC coating layer and the roll base material.

  In the work roll of Comparative Example 4, the surface of the forged steel work roll is placed in a plasma CVD film forming apparatus to form a DLC coating layer having a composition of ta-C: H type (hydrogenated tetrahedral amorphous carbon). Filmed. The work rolls of Invention Examples 1 to 7 were prepared by inserting the forged steel work roll surface into a plasma CVD film forming apparatus and forming an intermediate layer shown in Table 1, and then forming ta-C: H type (hydrogenation). A DLC coating layer having a composition of (tetrahedral amorphous carbon) was formed. In Invention Example 6, 0.05 μm-thick SiC was deposited after forming 0.05 μm-thick Cr as the intermediate layer. In Invention Example 7, 0.05 μm was formed as the intermediate layer. After forming Nb with a thickness of 0.05 μm, TiC with a thickness of 0.05 μm was formed. In any example, the film thickness of the DLC coating layer was 2.0 μm, and the ratio (sp3 / sp2) was 75%. In any example, a uniform DLC coating layer was formed on the surface of the work roll.

  About said work roll, adhesiveness and nano hardness were measured and evaluated. The results are also shown in Table 1. In addition, the shape of the work roll was the shape shown in FIG. 2, the body length of the roll part was 1,000 mm, and the diameter of the roll part was 80 mm.

<Adhesion (scratch test)>
A diamond stylus with an outer diameter of 200 μm is scanned with a load of 0 to 100 N at room temperature, a scanning speed of 10 mm / min, and a load speed of 100 N / min. The load value at the time when peeling or destruction of the protective layer is confirmed is compared, and the lower load value is defined as “adhesion”.

<Friction coefficient>
The dynamic friction coefficient (load 5 N, sliding of SUJ2 ball) evaluated by the Bowden method was obtained and used as the friction coefficient.

<Nano hardness>
Nano hardness was obtained by the nano indentation method. That is, for measuring the nano hardness, a nano indenter (manufactured by Agilent Technologies, XP / DCM) was used. Indentation indenter: Measured under the following conditions using a diamond Barkovic mold. Indentation method: continuous stiffness method, load: 200 μN, vibration frequency: 45 Hz, vibration amplitude range: 2 nm, maximum indentation depth: 500 nm, room temperature, average of 15 measurement points (interval is 70 μm), hardness at indentation depth of 200 nm Therefore, it was defined as nano hardness.

  As shown in Table 1, in Comparative Example 4 in which the intermediate layer was not provided, the adhesion strength remained at about 30 N, but in Invention Examples 1 to 7 in which the intermediate layer was provided, the adhesion strength exceeded 40 N. It was.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to prevent adhesion of the work roll surface, peeling of the DLC coating layer formed in the work roll surface can be prevented effectively. For this reason, the roll for metal plate rolling of this invention can maintain the surface property of a to-be-rolled material for a long time.

DESCRIPTION OF SYMBOLS 1 Work 2 Intermediate | middle roll 3 Backup roll 4 Work roll 4a Roll part 4b Small diameter part 4c Large diameter part 4d Sliding part 40 Diamond-like carbon coating layer 41 Base material part 42 Intermediate layer

Claims (4)

A roll used to roll a metal plate , containing 99.5% by mass or more of Ni ,
A roll substrate;
A diamond-like carbon coating layer with an amorphous structure in which diamond bonds and graphite bonds are mixed,
An intermediate layer made of metal carbide or pure metal formed at the adhesive interface between the roll base and the diamond like carbon coating layer ;
The intermediate layer is made of silicon carbide;
The diamond-like carbon coating layer, that having a composition of hydrogenated tetrahedral amorphous carbon,
Roll for rolling metal sheets.   The roll for metal plate rolling according to claim 1, wherein a friction coefficient of the surface of the diamond like carbon coating layer is 0.15 or less. The diamond-like carbon coating layer has a thickness of 1 to 10 μm.
The roll for metal plate rolling of Claim 1 or 2.   The diamond-like carbon coating layer has a crystal ratio of a carbon compound having a diamond-type crystal structure and a carbon compound having a graphite-type crystal structure, and a ratio of the carbon compound having the diamond-type crystal structure is 60 to 80%. Item 4. A roll for rolling a metal sheet according to any one of Items 1 to 3.